The Presumed Dead

During a walk, Mr Holmes unexpectedly receives a telegram with the following content: "Dear Mr Holmes. In recent weeks, incredible incidents have been mounting at the retirement home in Chiswick. Staff and residents are thoroughly frightened. I explicitly request your highly esteemed help! Signed, a companion." A few days later, the first unsolved murder occurs in said retirement home. Holmes reluctantly allows Inspector Lestrade, Inspector Wolfford and his landlady Alice to persuade him to take on the case. Under an assumed name, Holmes himself moves into the retirement home and begins to investigate. Eventually, he must face his own past and fears. And then there's also the question: Who is the mysterious companion from the telegram?