The steam launch in The Sign of the Four is named the Aurora. Holmes learns that the missing boat belongs to the boatman Mordecai Smith and uses the Baker Street Irregulars to search for it along the River Thames.
The Aurora is described as a fast, neatly kept launch painted black with two red stripes. Its funnel is black with a white band. Jonathan Small, travelling with the islander Tonga, has hired the boat while escaping with the treasure connected to the Agra Fortress.
Holmes and Watson eventually locate the Aurora and pursue it in a police launch. During the chase, Small throws the jewels into the Thames rather than allow the treasure to be recovered. The launch runs aground, and Small is captured, although the treasure itself is lost.
The Sign of the Four was Arthur Conan Doyle’s second Sherlock Holmes novel. It was first published in 1890 and introduced Mary Morstan, who becomes an important part of Watson’s personal story.