Usami Kei is a salaryman who has risen in status due to his engagement with Mei, the wealthy daughter of his company's president. Shortly after she breaks off the engagement, a power failure leaves him stuck in the elevator of his apartment building. Trapped with him are three others living on the same floor - Airu, a trilingual interpreter, Ojiro, a model photographer, and Masato, a psychiatrist. While waiting, their conversation hits upon their love lives and the question of whether there is truly only one fated partner for everyone. As a result, they decide to try "shuffling" their relationships with each other.

Plot: “Kagi no Kakatta Heya” is based on a novel by author Kishi Yusuke. Ohno plays an employee of a major security company who has to unravel various incidents. The series falls under the “locked room” mystery genre, in which crimes are committed under seemingly impossible circumstances (such as within a room with no apparent means of escape). Ohno’s character has an obsession with studying keys and locks, giving him an advantage in solving each mystery. -- Tokyograph