S1·E9 The Tragedy Of MH

One night, Nezu is attacked, leaving behind a 'dying message' supposedly saying 'M.H.', which leads Milky Holmes to become murder suspects, with Henriette giving them until the next morning to prove themselves innocent. When Milky Holmes seek wisdom from a Ouija board they found, a bright light shines and Cordelia, Nero and Elly are possessed by the spirits of their ancestors, Cordelia Gray, Nero Wolfe and Hercule Poirot, who were supposedly trapped within the Ouija board. However, their takes on their case aren't particularly helpful. Sherlock is then possessed by Sherlock Holmes, who identifies the culprit as Sherlock's kohai, Sonia. She attempts to escape but is stopped by Holmes and Rat, who had only been playing dead. The detectives soon take their leave, leaving behind a message for Milky Holmes saying their toys will return after a great trial, while Sonia is transferred to another academy.