Erika Toda joins a law firm headed by Serizawa-san, on the first case she meets Enomoto Kei of Tokyo total security who unlocks Serizawa who has accidentally been trapped in a vault. Form thereon the trio solve 10 cases related to the locked room. Enomoto always makes a small scale model and thinks technically in terms of security and locks to solve cases, while Serizawa assists by hinting some circumstantial evidences. Serizawa is always ready to take credit of new found fame.