Arthur Morstan was Mary Watson's father. He was a senior captain of an Indian regiment, and was later stationed near the Andaman Falls. He disappeared mysteriously in 1878 after returning to England, an event which would prove to be related to the mystery in The Sign of Four. It is revealed that Captain Morstan suffered a stroke when confronting John Sholto over the fate of the Agra Treasure. Sholto, knowing he would be blamed for the death, chose to cover it up and disposed of Morstan's body with the help of his manservant, Lal Chowdar.