Knock Knock tells of a married man (played by Keanu Reeves) finds his life falling apart when two young girls appeared suddenly at his home.
The story begins when, Evan (Reeves) had to stay home to finish the job, while his wife and two children go on vacation to the beach. Amid heavy rain, he found the door of his house for the knock. As he opened, he found two beautiful girls (Ana de Armas and Lorenza Izzo) stand the cold in front of his door.
They were soaking wet, and ask permission to Evan to get into his house. Initially, he asked their permission to dry off and use the phone. But in fact, both of them in fact have evil intentions unknown by Evan.