Sheldon and Penny bond in Leonard's absence, and Koothrappali finds someone to share his heartache with. Elsewhere, while away at an out of town conference, Bernadette and Amy are hit on at the hotel bar.
Love is in the air when Amy convinces Sheldon to join her, as well as Howard and Bernadette, for a romantic train trip to Napa Valley to celebrate Valentine's Day.
McGee and Bishop head to Afghanistan when a local case is connected to a series of friendly fire deaths overseas. Kasie ventures out of the lab and joins Torres in the field to analyse additional forensic evidence.
Katie must overcome her fear of wearing a bathing suit in public to help Anna-Kat get over her own fear of water; Oliver gives Greg a makeover.
Jeff wants different stories to share with Russell and Adam, and so he comes to Audrey about creativity in the bedroom. Meanwhile, Russell realises he knows nothing about his date.