On a Sunday morning in a park, Shinichi Kudou is approached by a man who asks whether Shinichi saw him there at the same hour the previous Thursday. The man says his grandmother died that Thursday morning and the police now suspect him of killing her, though he claims he was in the park the whole time. Intrigued, Shinichi insists on helping him establish an alibi and convince the two detectives watching him that his story is true. This single-episode OVA is a promotional side story for the twelfth Detective Conan film, offering a glimpse of that movie's backstory, and mixes mystery with comedy.