In contrast to Jekyll, the "metaphysical" scientist and his interest in releasing "evil" spirits which become physically alive, taking over the body and soul of their owner and embodying it in their own misshapen representations, Lanyon is a "traditional" scientist — completely uninterested in "the other world." Once, Lanyon and Jekyll were fast friends, but when Jekyll became too fascinated with delving into the darker aspects of science, Lanyon broke off their friendship — about ten years before the novel begins.
Lanyon is questioned keenly by Utterson about Jekyll, but Lanyon will say nothing definite, just that Jekyll is interested in the perverse aspects of science, and for that reason, he is no longer friends with him.
Finally, Jekyll/Hyde decide to take their revenge on Lanyon for his prudish denunciations of Jekyll; Hyde arranges a metamorphosis to occur before the good doctor Lanyon. Lanyon is so horrified that Jekyll has been successful in releasing his own evil that Lanyon cannot face the thought that there resides a similar Edward Hyde within him; three weeks after Hyde's contrived baiting of Lanyon's curiosity, the meek doctor is dead of shock.