Nash and company are at the airport waiting for "The Tourist," a notorious Russian assassin named Rychek, to appear. Rychek's target is FBI agent David Katz, but his gun jams. Nash and company give chase. Rychek flees, but not before shooting a security guard blocking his way. Nash runs into a woman who turns out to be ex-wife No. 1, Lisa. Lisa has returned from Paris.
Katz was given a phony tip to appear at the airport; the gun, a Glock 17, was hidden in a trash can by a janitor. Lisa reveals that she is getting married, and further that she and Nash are technically still married through some mix-up in paper work. At the courthouse, the marriage license secretary Tricia is upset that Nash and Lisa's 12 year marriage was ended.
At the new land-based SIU headquarters, Harvey discovers Katz's latest case of a credit card fraud ring. The janitor is identified as Stefan Bronski. Joe goes to retrieve Katz at his home, but a Claymoore mine blows up Katz's porch. Katz finally fesses up that his latest case is an undercover sting operation against a phony credit card dealer named Seth Wiley.
Harvey, Evan, Joe, and Katz arrest and interrogate Wiley. Wiley is hypo-allergenic to everything, so Joe gets Wiley to talk by threatening to smear dog saliva from Harvey's dog into Wiley's hair. Wiley reveals that the assassin Rychek was hired by a broker named Papazian. Papazian was to trade phony credit cards to the Ukrainian mob in exchange for a Foxtrot submarine. Papazian then planned to sell the submarine to a drug cartel in Columbia. The cartel was to use the submarine to smuggle cocaine into the US.
Meanwhile, Nash and Cassidy meet Henri, Lisa's fiancé over lunch. Henri is a celebrated French chef which greatly impresses the waiter. Upon returning from lunch, Nash discovers a book for naming babies on Evan's desk and mistakenly believes that Cassidy may be pregnant (the book is for ideas to rename Harvey's dog). Harvey and Evan discover the dead body of the janitor Bronski, killed moments earlier by Rychek with a pencil.
Nash and Lisa go to confront Cassidy at her dorm. Lisa is out, so the couple wait at a romantic setting by the Golden Gate bridge. They have sex on the hood of the 'Cuda. Cassidy realizes the situation immediately and is outraged that her parents are asking her if she is pregnant. Joe also discovers Nash's sexual activity by the evidence left in and on the 'Cuda.
Katz is secured at a Bed and Breakfast Inn, but gives away his location to Rychek, who is monitoring his cellular phone call from Katz's sister. Katz is alerted, along with Joe and Evan. They discover a booby-trapped pot of flowers addressed to Nash. Papazian is arrested red-handed with manuals and map routes for the submarine. Nash uses Ronnie, an SF uniformed officer, as a phony KGB agent to bluff Papazian to cancel the contract on Katz.
Lisa realizes she still loves Nash, but Nash tells her to go back to Paris with Henri. But Henri has left Lisa, but she will still return to Paris. Nash and Lisa part painfully at the airport. Nash is paid a visit by Rychek in the 'Cuda. With the contract on Katz cancelled, the upset Rychek decides not to kill Nash. Nash drives away.
For more, see commentary for Episode 60