When married couple Simon (Jason Bateman) and Robyn (Rebecca Hall) unexpectedly encounter Gordo (Joel Edgerton), an acquaintance from Simon's past, little do they know that their perfect lives will be thrown into a terrifying tailspin. At first, Simon doesn't recognize Gordo, but after a troubling series of uninvited encounters and mysterious gifts, a horrifying secret emerges. As Robyn learns what really happened between Simon and Gordo, she begins to question how well she knows her spouse.