When Chuck and Sarah go undercover in Milan, Chuck realizes the "Achilles' Heel" in their relationship, but must set personal issues aside for the mission. Meanwhile, Morgan recognizes a fatal flaw that compromises the new Buy More. Elsewhere, Casey struggles to put down roots in Burbank.

Chuck and Sarah work on becoming better communicators as they join Awesome and Ellie for a getaway to Costa Gravas. There, the gang is reunited with Generalissimo Goya who finds himself in a dangerous situation once again. Back at home, Morgan embarks on a forbidden romance that may put him at odds with Colonel John Casey.