The series is described by its creators as a sequel to the 1886 novella "Strange Case of Dr Jekyll and Mr Hyde", rather than an adaptation of it, with the Robert Louis Stevenson tale serving as a backstory within the series. It stars James Nesbitt as Tom Jackman, a modern-day descendant of Dr. Jekyll, who has recently begun transforming into a version of Mr. Hyde (also played by Nesbitt). Jackman is aided by psychiatric nurse Katherine Reimer, played by Michelle Ryan. Gina Bellman also appears as Claire, Tom's wife.