The film tells the fictional story of Sandy Patterson (Jason Bateman) whose identity is stolen by an unnamed woman (Melissa McCarthy). In Denver, Sandy Patterson buys identity theft protection from Diana, a con artist, over the phone and reveals all of his personal information. At work, after Sandy clashes with his obnoxious boss, Harold Cornish, he receives a phone call that reminds him he has an appointment at a salon in Florida. Confused, he puts it out of his mind when co-worker Daniel Casey suggests they and several others start their own firm; Sandy agrees to join them.
When paying for gas, Sandy's card is declined, and the clerk cuts it up. As the credit card company tells him that he has spent much money in Florida, he is arrested for missing a court date there. At the police station, Detective Reilly determines Diana has stolen Sandy's identity. The situation worsens when cops ask Daniel, now his boss, about Sandy's possession of drugs. Reilly says Sandy's name was used to buy drugs from someone named Paolo. When the cops say they can do nothing unless the identity thief is in Denver, Sandy offers to retrieve her and convince her to clear his name despite his wife's concerns. He finds her at the same time crooks are also after her and break into her house. They escape and after traveling through several states, and having various escapades and the criminals continue their pursuit of Sandy and Diana. The pair con an accounts processor and steal Sandy's old boss - Cornish's identity to create new credit cards. In St. Louis, the two share dinner, and Diana admits she does not know her real name. As a baby, she was dumped outside a police station and spent her childhood in foster care, fending for herself from a young age.