When Barney is about to complete the perfect week - landing seven different girls in seven days - the gang roots him on in order to forget about their own miserable week.
The gang tries to help Ted when the perfect girl is finally available, and Marshall takes action when he finds a letter written by his younger self.
In the sixth season finale, a new lead in a cold case requires Lisbon to delay her plans to leave for Washington, D.C. with Marcus Pike, giving Jane time to finally come to terms with his feelings for her and decide on a course of action.
When ballistics tie a recent murder case of Rush's to a serial killer who was seemingly inactive for 27 years, Diane Yates, a tough, no-nonsense FBI agent who was responsible for the end of Stillman's marriage, shows up to enlist the team's aid in finding the killer who has eluded her for 30 years.
In the conclusion of this two-part episode, after determining the serial killer's identity -- and some of his likely future targets -- the team and the FBI work together to apprehend him while trying to locate and protect the people he's preparing to kill.
