There's a new writer in town and he has his eye on Beckett. More on that later. Right now, Castle and Beckett investigate the death of a swimmer who had a shot at the Olympics. Zack Lindsey was found in a pool after a late night training session. His swim team is led by Coach Rome, who says Zack recently won a meet even after a bout of food poisoning. Nothing could keep that kid out of a pool. Well, nothing short of murder.
Olympic swimmer "Rocket" Rob Tredwick trained with Zack the night he was murdered. Both guys struggled to make it, so Rocket Rob took Zack under his wing. He says the kid recently broke up with his girlfriend, Bridget McManus. The jilted girl was upset about getting dumped, but she's no killer.
A stash of anabolic steroids is discovered at Zack's trashed apartment. The victim was clean, so maybe he was dealing. Alex Conrad suggests the steroids are a red herring. Who is Alex Conrad, you ask? Well, he's that writer we mentioned earlier. Castle considers him his protege. Beckett considers him a fresh set of eyes. In other words, she thinks he's right about the steroids. The real killer could be from Zack's old neighborhood.
Zack and best friend, Tommy Marcone, stole cars to make ends meet. One of the vehicles found in a chop shop belongs to Zack's rich rival teammate, Brian Morris. Castle finds a vile on the front seat. The steroids found in Zack's place belonged to Brian. If Zack was going to turn in his teammate, it's a pretty good motive for murder. Too bad Brian has an alibi.
Castle doesn't believe a pampered person like Brian has the guts to commit murder. He could have hired someone though. This brings Castle and Beckett back to Tommy Marcone, who recently became $25,000 richer. But Tommy didn't kill his BFF. That money came from a blackmail scheme. Zack had no idea his buddy was doing any of this. Tommy fears his actions may have gotten his best friend murdered.
Castle believes Alex Conrad is making a move on his muse. He promptly removes his glowing review of Alex's debut novel from RichardCastle.net and replaces it with cover art for Heat Rises. In an attempt to keep his protege away from Beckett, Castle invites Alex to his poker game with Michael Connelly and Dennis J. Lehane. The seasoned novelists pick apart the rookie writer's theories about Castle's case. Classic stuff!
The poker conversation sparks a theory with Castle. He believes Coach Rome would have a lot to lose if it came out that his swimmers were juicing. The coach cops to the drug charges saying that Brian's dad approached him to make his son the best he could be. Coach Rome had gone down this road once before with another swimmer: "Rocket" Rob Tredwick.
When Rocket Rob realized protege Zack may expose the steroid scandal, he would lose all his medals and fame. Castle says, "The one man Zack thought he could trust, his mentor, turned out to be his killer." Speaking of mentors, Beckett gets Castle to admit that he was jealous about the time she was spending with Alex Conrad. Well, those days are over. Beckett says, "From now on I am a one writer girl." Nice.