The BAU travels to Boston when the serial killer from one of Agent Hotchner's first cases, which involved one of the most notorious murderers in the history of New England, returns after 10 years.
A covert identity created for one of Gibbs' undercover cases 20 years ago resurfaces after a murder victim is found living under the alias.
The team bumps heads with Lt. Lynch when she signs them up for an off-book undercover operation to take down a local gang printing counterfeit money without giving them enough time to prepare for the mission. Also, tensions rise at home for Hondo as his parents' strained relationship becomes worse.
While investigating the murder of man hired to make dirty bombs that terrorists intend to set off in Miami, Horatio finds the bloody fingerprint of his brother, Raymond, who he believed to be dead.
When the 1958 suicide of a celebrated Philadelphia disc jockey is discovered to have actually been a murder, Rush and the team must find the truth of this public persona's private life by decoding a message hidden in his final broadcast.