Bartholomew is found dead in his home from a poisoned 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 steam launch named the "Aurora". With the help of dog Toby that he sends Watson to collect from Mr. Sherman, the Baker Street Irregulars and his own disguise, Holmes traces the steam launch. In a police steam launch Holmes and Watson chase the "Aurora" and capture it, but in the process end up killing the "small" companion after he attempts to kill Holmes with a poisoned dart shot from a blow-pipe. Small tries to escape but is captured. However, the iron treasure box is empty; Small claims to have dumped the treasure over the side during the chase.