Chuck and Sarah travel to fashion week in Milan to retrieve a high-tech secret weapon. While they are undercover, Chuck realizes what the "Achilles' heel" is in their relationship, but he 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. KAROLINA KURKOVA (The Victoria's Secret Fashion Show), LOU FERRIGNO (The Incredible Hulk, The King of Queens), ISAIAH MUSTAFA (upcoming Horrible Bosses, Madaea's Big Happy Family) and BRONSON PINCHOT (Perfect Strangers, Beverly Hills Cop, Step by Step) guest star.