In the season finale, all three couples, Tom and Trina, Roger and Janet and Bruce and Susan, face decisions about their respective marriages as they attend the Deckers's end of summer clambake party.

The Task force believes the Bay Harbor Butcher case is closed, but Dexter still has some trouble to deal with.

It is graduation day for Ryan, Seth, Summer, and Marissa at Harbor High School. After graduation they all go out to eat and celebrate their graduation. Ryan's mother gives him a new car as a graduation present. Marissa is going to spend a year on a boat with her father as her graduation gift. Seth finally gets into RISD for second semester. Summer is still going to Brown University in the fall. Volchok is still mad at Marissa and Ryan, so he decides to crash Ryan's car.

Homer is first revealed to be impotent because of the nuclear plant, so Homer is rewarded with an award for "Excellence in the field of Excellence". Homer's half-brother Herb Powell returns, but this time not as a successful businessman. After Homer wrecked his car company, Herb has become a bum, but with a little help from Maggie, he thinks he has come up with a shoo-in invention that will put him back on top. Herb wants to build the first baby translator, a device that will interpret babies' cries and mumbles into plain speech. Homer agrees to fund the research ...

Dan’s newest mission requires him to deal with a man who claims he’s a time traveler. While Livia finds herself on a separate mission too, just before her wedding to Henry. Meanwhile, Jack talks to Elliot Langley, and Katie thinks that Dan has been wounded again after she discovers blood in the house.

The BAU faces one of its toughest cases when the team is called to New York City to determine if a series of random shootings is the work of one serial killer or a team of killers working together.