By the way, Doctor, I shall want your cooperation.' 'I shall be delighted.' 'You don't mind breaking the law?' 'Not in the least.' 'Nor running a chance of arrest?' 'Not in a good cause.' 'Oh, the cause is excellent!' 'Then I am your man.' 'I was sure that I might rely on you.

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.