Spencer (ASHTON KUTCHER) is a government assassin, who hates his job and craves a normal life. He gets his chance when, on assignment in France, he meets a slightly neurotic American woman named Jen (KATHERINE HEIGL), who has just broken up with her boyfriend and is on holiday with her parents, the Kornfeldts (TOM SELLECK and CATHERINE O'HARA). Spencer's boss, Holbrook (MARTIN MULL), tries to convince Spencer to stay, telling him one never really leaves his line of work. But Spencer is adamant.
Flash-forward three years, and Spencer and Jen are happily married, living in a big house, and surrounded by the usual assortment of suburban character types: Lily and Mac, a nerdy, young couple (ALEX BORSTEIN and KEVIN SUSSMAN); Henry, the boorish, overgrown frat boy (ROB RIGGLE); Vivian, his attractive co-worker (KATHERYN WINNICK); Olivia, a flirty housewife (LISA ANN WALTER); Kristen, the cynical best friend (CASEY WILSON); and so forth.
Someone, though, puts out a hit on Spencer's life. He learns that there is a $20 million bounty on his head, and he is forced to tell Jen the truth. On the run, Jen and Spencer soon learn that pretty much all of their former friends and neighbors are "sleeper assassins" placed in close proximity to them just waiting to be "activated." On top of that, Jen is also cranky and nauseous, which can only mean one thing. She's pregnant. Can Mom and Dad help? Or are they assassins, too?