Robert Louis Stevenson’s classic novella, The Strange Case of Dr. Jekyll and Mr. Hyde, published in 1886, is the well-known tale of a respected scientist (Dr. Henry Jekyll) who transforms himself into an evil-doer (Mr. Edward Hyde). While the work raises issues of tort and criminal liability, this article analyzes the legal issues presented by one particular and crucial plot device that Stevenson employs—the last will of Dr. Jekyll. This will so obsesses Jekyll’s friend and solicitor, Gabriel John Utterson (through whose eyes the story unfolds), that he is impelled to seek the truth behind his friend’s relationship to Hyde. At the end of Utterson’s search, the solicitor learns about Jekyll’s dangerous scientific experiment. This discovery leads to the respected doctor’s moral downfall and his physical death.

This article is presented as an imagined dialogue between the article’s author and Utterson, Jekyll’s lawyer, concerning the issues surrounding Jekyll’s mental capacity to make the will that left the doctor’s estate to Hyde. Jekyll’s will is an excellent case study for the application of various legal rules and doctrines regarding a testator’s mental capacity to make a valid will. These rules include those relating to the general soundness of the testator’s state of mind, the issues of undue influence and duress, and the doctrine of insane delusion. Stevenson’s novella is a wonderful vehicle for examining important legal problems that remain as relevant in America today as they were in England during Queen Victoria’s reign.