We open on a Seabird's Minor League baseball game in which the batboy, Young Shawn, is seen idolizing the star player Cal Eason.
We then cut to present day. Shawn is playing in a police league softball game for the SBPD. Henry is the umpire and calls Shawn out at home plate, thus causing them to burst into a shouting match. There is definitely some leftover tension between Shawn and Henry from his Little League days. Henry ends up throwing Shawn out of the game.
After the game, Shawn is shocked to see Mel Hornsby, the Coach of the Seabirds, walking toward him. Mel tells Shawn that his bench coach, Grady, suddenly died of a heart attack, but he believes there was foul play at hand. Grady's system had amphetamines in it, and Mel knows that Grady would have never put his weak heart at risk by doing drugs. Mel hires Shawn to investigate and appoints him as hitting coach for the Seabirds as a cover. This excites Shawn, and the fact that his idol Cal is back on the team is icing on the cake for him. Shawn gets Gus to join the investigation disguised as the team Mascot, forcing him to suit up in an enormous, flea-infested Seabird costume.
Shawn and Gus go to Grady's house. There, Shawn takes a swig out of a sports water bottle sitting on a table in the living room that is, not to his knowledge, laced with amphetamines. With Henry's help, Shawn figures it out that the sports drink belonged to the Seabird's top player, Izzy, and not to Grady. Their bottles got switched at hitting practice on accident.
Shawn and Gus go to find Izzy at a bar the players frequent. They determine that Izzy is clean and isn't the one taking amphetamines to boost his performance on the field like they had thought. Then Shawn and Henry put it together that someone who wanted Izzy off the team tried to get him busted for drug use by spiking his sports bottle... but who? They run into Cal Eason at the bar, who relays to Shawn and Gus that he would do anything to get himself back into the majors as a first basemen instead of a catcher, as his knees are starting to go. But Izzy, the 1st baseman and star player, is overshadowing him.
With Henry's help, Shawn puts it together that if Izzy were caught with drugs in his system, he would be suspended, thus creating an opening for Cal to take Izzy's playing time. Shawn approaches Cal during batting practice and accuses him of trying to drug Izzy, but Cal denies it.
Back in the dugout during a game, the General Manager of the team steps in and asks why Izzy isn't playing. Mel says it's because of Izzy's attitude problem. But the GM makes it clear that he wants Izzy playing no matter what. And with that, Izzy is put back in the game.
Shawn watches Izzy at bat. Shawn predicts the next pitch, and is spot on. Shawn predicts the following pitch and, Mel, impressed by Shawn's abilities, tips the 3rd base coach who then tips Izzy what the next pitch will be. As a result, Izzy hits a homerun, and Shawn sees Izzy making eyes at a fellow player's wife who is sitting in the stands cheering for him. Shawn then thinks it must have been this particular player that found out about Izzy sleeping with his wife and tried to get him suspended.