Rather than attempt to reduce Siryn's really quite fascinating family into a few quick synopses and character bios, I'll do my best in telling you the history of the Cassidys of County Mayo.

Sean and Tom Cassidy were cousins born in County Mayo, Republic of Ireland, and grew up in the family's ancestral fortress, Cassidy Keep. Sean went to Trinity College and later went into law enforcement. In his career he would serve in INTERPOL, the NYPD, and eventually join the X-Men as Banshee. Tom went to Oxford and would later become an international black market criminal. The bulk of the family's money was apparently spent many years before the cousins were born, but the castle remained in their possession. Tom was the older of the cousins, and initially the heir to Cassidy Keep, but in their young adulthood, gambled his inheritance in a game with Sean and lost. Thus Sean became the owner of the Keep. Both of the cousins' parents died before Theresa's mother came into the picture.

Sean met Maeve Rourke on the way home from a concert in County Londonderry, Northern Ireland. He was pulled over by some corrupt cops, and Maeve came by and rescued him on her motorcycle. The police gave chase while Maeve raced them towards the Republic. On the way south, Maeve lost control of the bike, sending her and Sean over a cliff. Sean used his mutant powers to fly himself and Maeve out of danger, stopping only when they'd reached Cassidy Keep, thus each rescued the other on the same night. Sean invited Maeve into the castle for a drink, where she also met Tom. Thus the tension began that would define the cousins' relationship to each other for years to come: Tom, a notoriously charming ladies' man, was just as smitten with Maeve as was Sean, a self-described "country lump." Maeve, a university student studying History, liked them both, and in fact dated both of them for some time after that first meeting.

The turning point came when Maeve invited Sean to escort her to a dance at her school. Sean was just as excited as could be, trussed himself up into a hilariously ugly maroon bell-bottom suit, and got on his motorbike to ride through much of the same set of roads he'd taken home from that Londonderry concert. The same corrupt policeman recognized him, this time to determined to nail him, and gave chase until he managed to run Sean and his bike off the road. A wounded Sean managed to get himself back home to the Keep, where a duly alarmed Tom and their housekeeper, Mrs. Bridges, put Sean in bed and called for a doctor. Sean asked Tom to escort Maeve in his place and tell her what had happened.

Tom showed up at Maeve's dormitory at his dapper best, and initially told Maeve simply that Sean wasn't coming, thus leaving her to speculate that Sean had merely stood her up. It could have been an opportunity to get the upper hand over his cousin in the race to win Maeve's heart, but while dancing the night away, Tom felt guilty and gave up the game. He confessed that Sean was injured and had tried to come. That was the night when Maeve decided that Tom was her "dearest friend," but Sean was the man she loved. The irony of her choice was that Tom loved her more than any other woman he'd known, while Sean had a history of no luck with the ladies. Sean, despite being a sincere, honest, productive and perfectly good-looking man with a good job, had no confidence in meeting women, whereas Tom could attract the ladies with no problem at all, but Maeve was the only one he really loved. How ironic, then, that she was the only one he couldn't have.

Sean and Maeve eventually got engaged, and Tom served as best man at their wedding. It's no surprise that the pictures of the wedding party at the altar show Tom looking rather unhappy. The course of Sean's life would have gone very differently indeed if not for his work with INTERPOL. They were only married a little while--let's say a month, perhaps?--when Sean had to leave on a mission that would take him away from home for an unknown period of time and make him unable to contact his wife. So he left his wife at home with his jealous cousin, where she soon thereafter found out she was pregnant. Tom presumably took care of Maeve during her pregnancy, and Sean was still out of the country and out of contact when she gave birth to Theresa.

He was still away, too, when Maeve took her baby daughter up to Ulster for a visit to relatives, where she was killed in an IRA bombing. Tom found Maeve's body, took a relatively unharmed Theresa out of the wreckage, and Maeve was buried at a County Mayo church. After losing the love of his life, Tom looked after Theresa until Sean came home. Thus, Tom was charged with the job of telling Sean that his wife was dead, and I suppose you can imagine how Sean felt to come home from a year-plus-long INTERPOL mission and find out he'd just become a widower, after having so little time with his wife in the first place. Sean was devastated, and in his anger, used his power to attack his cousin before Tom could tell him about the baby girl waiting for him in the castle. Tom was blown onto a cliff and broke his leg so badly he was left with a limp and started walking with a cane. Sean flew off without knowing his wife had been pregnant the last time he'd seen her.

Now if you'll excuse me for a bit of fannish speculation, my question at this point in the saga is: Where were the Rourkes? Surely they didn't all get blown up in the same attack as Maeve? Did she have parents? Siblings? What did they have to say about baby Theresa being left without a mother? Did any of them offer to raise her after Sean flew off? What did they learn about Maeve's bereaved husband taking off again as soon as he'd come home?

Regardless of their opinions of the goings-on in County Mayo, the Rourkes were apparently not heavily involved in Theresa's childhood, and Tom took it upon himself to raise her. He did not attempt to contact Sean after the incident, and Sean, for his part, did not attempt to return to Cassidy Keep for years after. Tom was probably already involved in the black market by that point, and while raising Theresa, who called him "Uncle," told her that her father was dead. Therefore, Theresa never got to know her mother, grew up thinking she was an orphan, and while her uncle wasn't at home being her single parent--and, by all accounts, taking very good care of her--he was making money by breaking the law.

Tom loved Theresa just like his own daughter, but also became increasingly immersed in his illegal activities, so when she was twelve, he sent her off to boarding school to keep her insulated from his career. This was the place where Theresa didn't know her uncle's reasons for sending her off, thus thought she was being punished, and took up the bottle. It was also during this period of her life that Sean, having been tracking Tom's activities for INTERPOL for quite some time, returned to Cassidy Keep and had Tom arrested for black marketeering. Theresa was fifteen then, and when she heard of Tom's arrest, started drinking more heavily. She read about the trial in the newspapers, but she didn't attend the trial or go to visit Tom in prison, an omission that would leave her feeling guilty for years afterward.

Sean was still devastated over losing Maeve for years afterward, and first encountered the X-Men as a villain code-named Banshee, but he soon turned to the right side. In the mean time he also left INTERPOL and did a stint with the NYPD. He eventually joined the X-Men alongside Wolverine, Storm, Colossus, Thunderbird and Sunfire.

Tom didn't have his niece to visit him in prison, but he did make a friend: he met Cain Marko, the Juggernaut. The two became best friends and together escaped from prison and started antagonizing the X-Men, particularly Banshee. After that point, Tom was apparently not so interested in keeping Theresa insulated from his career, and--was she still in school then? I'm not sure--took his niece, who had inherited her father's mutant power, to San Francisco for a crime spree. This move became a turn of good luck for Sean and lousy luck for Tom. Theresa was at this time extraordinarily powerful--really, folks, go find Spider-Woman #37-38 and see the crazy shit this girl could do with her voice--but didn't have the stomach for murder and mayhem. Well, okay, maybe she later developed a stomach for mayhem under Cable's tutelage, but she wasn't up for killing, and it was because of this squeamishness that Spider-Woman was able to get the upper hand. Black Tom, Juggernaut and Theresa, now called Siryn, were brought down by Spider-Woman and the X-Men, and Siryn was carried away unconscious by paramedics. Black Tom told the X-Men that his niece wasn't responsible for the crime. He wrote a letter for Sean, explaining the girl's existence. Sean was by this point temporarily de-powered after a battle with Moses Magnum and was in love with Dr. Moira MacTaggert, the noted geneticist. The X-Men promptly introduced him to his daughter: he read the letter she gave him from Tom and was overjoyed to meet her. (See Uncanny X-Men #148) Thus Tom was estranged from the girl he'd raised from infancy while Sean suddenly had a teenaged daughter in his life.

Sean took Theresa to live with him and Moira on Muir Island, and, despite their joyous reunion, it was not all smooth sailing from there. I'm not quite sure what happened exactly, but there was a reference in an issue of Generation X to how Theresa had "hated [Sean] for not having raised her." She was certainly happy enough at their first meeting, but it makes sense that meeting your parent for the first time when you're well into your teens would cause some awkwardness at the very least. Perhaps Sean tried a little too hard and too soon to play Daddy, and Theresa did not take kindly to such behavior from a guy who wasn't around when she was little. It wouldn't really have mattered whether she blamed him for his absence, the point being that he was in no position to make her his little girl. Sean later remarked to Theresa something along the lines that perhaps it was too late for them to be father and daughter, but they could still be friends. (X-Force #35) Moira, also, found Theresa's presence rather threatening and therefore felt somewhat insecure to have her in the picture. Moira was unwilling to have children with Sean, because her own son, Kevin, became the mutant monster known as Proteus, and of course she knew this wasn't Theresa's fault, but still Theresa represented something that Moira couldn't give Sean. Maybe that competition, also, caused an issue or two. Whatever it was, it seems to have worked itself out eventually, and in time they muddled together a very warm relationship.

Theresa lived on Muir Island until shortly after the Shadow King saga, which left her so traumatized she needed to find a new home and new friends. She teamed up with X-Force while running up against Black Tom and Juggernaut during their attack on the World Trade Center. Banshee was not happy about her joining X-Force, but there was really nothing he could do about it.

Black Tom was badly injured during that fight with X-Force and Spider-Man, during his and Juggernaut's attack on the WTC. To treat his injuries, he was taken to some odd scientists in France who put him back together by introducing a plant-growth organism into his body which put him physically in working order but didn't do anything good for his mental health. Black Tom and Juggernaut subsequently showed up at Cassidy Keep to find Michael Flaherty, the family lawyer, occupying the castle, and Tom, not taking kindly to this, attacked Flaherty and landed him a hospital stay. This was just before Theresa showed up at the Keep with James Proudstar after he confronted her about her drinking problem, so I guess you can imagine the timing for both of these adventures was not ideal. Juggernaut and Proudstar arranged for Theresa and Tom to visit Maeve's grave on the same night. Theresa, for her part, berated Tom for blaming everyone but himself for all his wrongdoings and instability, but acknowledged that she also remembered how he'd raised her, and she still loved him as her Uncle. Tom accepted the blame for not raising Theresa to be happy, but for that, Theresa insisted there was no one responsible but herself. She decided that she couldn't keep on recriminating Tom for the mistakes he'd made, and then go and repeat them herself. She poured out her flask and hasn't had a drink since. Tom was arrested that night, and at that moment went quietly, but of course by that time he'd already proven that he wasn't inclined to stay incarcerated for very long.

The plant-man graft continued to make incursions on Tom's physiology, making him even more deranged and unstable, and he soon decided that Deadpool was the way to fix the problem. He hired a team of mercenaries to capture Deadpool so that Tom could use his healing factor to restore his own health. Banshee and Siryn took that opportunity to try and capture Tom themselves, as they wanted Tom to get help, but not run loose. They teamed up with Deadpool and tracked down Tom and the Juggernaut, whom Deadpool convinced to cooperate with them so they, with the help of Dr. Killebrew, could save Tom's life. Banshee, meanwhile, was not comfortable with how Theresa was bonding with Deadpool, but, again, she was grown up and there was really nothing he could do about it.

Despite Killebrew's best efforts, Tom later got free again and became more plant-growth than man, completely off his rocker. He attacked the Massachusetts Academy, where Sean was now co-Headmaster of Generation X. In the fight that ensued, he railed at Sean that he was at fault for Tom's madness because Sean took Theresa away from him. (Tom, of course, had been trying to murder Sean for years before the latter found out about Theresa.) Penance sliced Tom in half, to which Sean said, "Good work, lass," but of course that wasn't the end of it.

Black Tom has shown up several times since then, appearing much more human and less tree, but still increasingly out of touch with reality. He is the epicenter of the Cassidy Family Insanity.

Sean went straight to San Francisco when he heard that Theresa had lost her voice from Feral's attack, but he didn't see her there. She spent most of that day wandering the city, teetering on the edge of suicide and drunkenness, and only came back to headquarters late at night. She handed James a letter, explaining why she was leaving the team and where she was going, said good-bye to him as much as one without vocal ability can do, and left without seeing her father. She went to live with Victoria Donnelly, a cousin of Maeve's, in the high desert of California. Victoria was a mystery novelist, and from what little we saw of her, a perfectly decent and sane woman, which begs the question again: where were the Rourkes during Theresa's childhood? Surely she has some sane relatives, somewhere. Theresa also turned down Sean's invitation to spend the following Christmas with him, which made her father sad.

It wasn't too much later that Moira MacTaggert died of the Legacy Virus, in response to which Sean took to drinking heavily. Due to Sean's alcoholism and Emma Frost's instability, the Massachusetts Academy was soon shut down and Generation X disbanded. Sean moved back to Cassidy Keep and eventually pulled himself together: he quit drinking and created the X-Corps, his own international mutant police force. Unfortunately the squad was composed partly of longtime supervillains, most notably the telepath Mastermind, whom Sean used to keep the other villains under control, and this did not turn out well. The good team members, such as Husk (Paige Guthrie, sister of Siryn's former teammate Cannonball), M (Monet St. Croix, Siryn's current teammate in X-Factor Investigations) and Multiple Man (head of X-Factor Investigations) were on Sean's side, but Mastermind ultimately was not. Mystique infiltrated the team, disguised as Multiple Man, and slit Sean's throat. He survived, but his mutant power was impaired, and more importantly, he had to live with the knowledge of his blunder. Theresa joined the X-Corporation's strike force in Paris in response to the X-Corps fiasco and was thoroughly annoyed with her father for his lapse in judgment.

Theresa didn't stay with X-Corporation for terribly long, while Sean eventually went back to the X-Men. Theresa eventually became part of X-Factor Investigations. Banshee's sonic scream never fully recovered from the injury that Mystique had inflicted on him, an issue that came to the fore when he tried to keep a madman from flying the Blackbird into a plane full of passengers. He tried to use his sonic scream to slow the Blackbird's flight, but instead the jet hit him head on, and Banshee was killed. Cassidy Keep and related assets are willed to Theresa, as he explains in a very sweet and touching DVD that he made for her (she initially thought it was Brigadoon, a movie he'd apparently been trying to get her to watch). Cyclops came to give Siryn the bad news, and handed her a package containing the DVD and Sean's tobacco pipe, which had been in the Cassidy line for generations. She was still unwilling to accept that Sean had died, and to this point is still in denial. And I can say that I do see the logic in her argument that half the X-folk are always mourning the other half but no one ever stays dead, but her behavior looks more like she's trying to convince herself he's still alive than that she genuinely believes what she's saying.

Tom was de-powered in the Decimation, has lost his Plant-Man powers, and is now serving a prison sentence. Theresa hasn't mentioned him in years. Banshee is dead. This leaves her with her uncle in prison, her aunt still, by all accounts, perfectly healthy but living on the other side of the country, and a baby on the way with a guy who has much more pressing matters on his mind than dealing with Terry. Yeah, if I were in her shoes, I wouldn't want to hear about my dad dying, either.