I have no pretence to greater physical courage than my neighbours, but familiarity with a subject robs it of those vague and undefined terrors which are the most appalling to the imaginative mind. The human brain is capable of only one strong emotion at a time, and if it be filled with curiosity or scientific enthusiasm, there is no room for fear. ("The Brown Hand")

He had maintained a platonic relationship with Jean while his first wife was still alive out of loyalty to her. A sequel to A Study in Scarlet was commissioned and The Sign of the Four appeared in Lippincott's Magazine in February 1890 under agreement with the Ward Lock company. Conan Doyle fathered five children.

He was a prolific writer whose other works include fantasy and science fiction stories plays romances poetry non-fiction and historical novels.