Lucas and Sami discovered they had similar interests: they both wanted Austin and Carrie to break up; Sami wanted revenge on Carrie, Lucas wanted Carrie to love him. The Brady-Roberts Alliance was formed when Lucas Roberts was rejected by Carrie and Sami was rejected by Austin.
It started like this: Sami was raped by Alan Harris, who was a West Point friend of Lucas and who had originally been interested in Carrie. Because Carrie was not a virgin, Alan shifted his attention to dating Sami with the intent of taking her virginity by force. After the incident, Carrie, distraught and trying to help, went to Alan's apartment and attempted to trick him into admitting what he'd done. Carrie discovered a shrine of herself in Alan's apartment, as well as a black ski mask that her own would-be rapist had worn at Green Mountain Lodge. She realized that Alan Harris was the same man as the man who'd attacked her. Sami discovered what Carrie was intending to do and raced to Alan's apartment to try and keep her out of danger. Alan held both of them hostage, but they were rescued by the police.
Alan was brought to trial but Carrie's disastrous testimony confirming Sami's reputation as a liar got him off the hook. He skipped town and Sami blamed Carrie for this, becoming determined to repay her sister by ruining her relationship with Austin. She wanted him because he gave her the benefit of the doubt and stood by her during the trial, something that no one had ever done for Sami before.
Alan later returned to Salem and fully intended to rape Sami again, but during their fight on the docks she got his gun away from him and shot him in the groin, disabling his "equipment" forevermore. (You go Lorena Bobbitt--I mean, Sami!) When Lucas visited Alan in the hospital, he got him drunk and got him to confess what he'd done. It was revealed that Alan was a serial rapist specializing in virgins, and once word of this got out he was sent to prison.
In a moment of mutual despair, they comforted each other in a Titan Publishing office. Austin was there that night and thought he saw Lucas and Carrie having sex. He was clued into his mistaken assumption by the evidence of Carrie's sweater lying on the floor, which Sami had "borrowed" earlier that night without Carrie's permission. Their night of passion resulted in William Robert Reed (a.k.a. William Robert Brady-Roberts), who Sami mistakenly believed to be Austin's son, conceived when she drugged Austin and took advantage of him in his weakened state and his belief that he was having sex with Carrie.
But is Will really Lucas' son?
That's the question bothering me the most. The blood tests could be inconclusive, and since we don't know what type blood Sami, Austin or Lucas have, I suppose we will never know unless they do DNA testing.
