Bartholomew is found dead in his home from a poison dart and the treasure is missing. While the police wrongly take Thaddeus in as a suspect, Holmes deduces that there are two persons involved in the murder: a one-legged man, Jonathan Small, as well as another "small" accomplice. He traces them to a boat landing where Small has hired a launch named the Aurora. With the help of his dog Toby and the Baker Street Irregulars and his own disguise, Holmes traces the launch.