Paddington station has been referred to in several popular works of fiction. It is mentioned in several Sherlock Holmes novels. In "The Hound of the Baskervilles", Watson and his companions Dr. Mortimer and Sir Henry Baskerville leave for Dartmoor from Paddington, while in "The Boscombe Valley Mystery", Holmes and Watson leave the station for a train to Boscombe Valley near Ross-on-Wye, Herefordshire. The mystery novel "4.50 From Paddington" (1957) by Agatha Christie begins with a murder witnessed by a passenger on a train from Paddington. One of The Railway Series books, "The Eight Famous Engines", contains a story about Gordon, Duck and a foreign engine debating which station London is. Duck says that he used to work at Paddington so he knows that Paddington is most important. However, Gordon later finds out that the station in London is St Pancras. There is a fictional underground Paddington station on the North London System in the novel "The Horn of Mortal Danger" (1980).