The Final Nail
Castle Season 3 Episode 15 (02/14/11)
Damien Westlake, an old friend of Castle’s, wife is murdered on this episode. When Beckett arrives on the scene, Castle is already there with his friend.
Beckett suspects Damien as the murderer, causing Castle to be defensive. Beckett tells him to go home, allowing him to work on Damien’s fathers unsolved murder case.
Money appeared to be motive for Damien, but it turned out to be the ex-husband’s girlfriend who had murdered Vickie Westlake. She was afraid of losing her boyfriend to his ex-wife who he had talked about getting back together with.
Castle figures out another classmate of theirs had killed Damien’s father after being paid by Damien. Damien is arrested. Castle is upset with the way things turned out and him and Beckett head out for a drink.