However, the other man, who begins calling himself Mr. Hyde (Nesbitt), takes over Tom's body more and more frequently. The dangerous Hyde is physically fast and powerful, and he has a mean streak that terrifies those who know him. Tom begins to find himself struggling to stay in control, while Katherine attempts to help him keep Hyde at bay.

Tom goes to see his estranged wife, Claire (Gina Bellman), and she admits she hired a private detective to see whether he was having an affair. The suspicious black van that appeared to be following him suddenly makes sense. Strangely, she doesn't learn of Hyde's activities, however. Confused, Tom tracks down the private detective, Miranda, only to discover that she knows Mr. Hyde all too well. As Tom attempts to confront Miranda, he learns she doesn't have a black van. Someone else is interested in the activities of Dr. Tom Jackman.

As Tom attempts to find out who the black van people are, Hyde becomes desperate to get out from under Tom's control. Hyde pays a visit to Tom's family. Claire believes Hyde is Tom's cousin. What else could account for the frightening resemblance?

When Tom wakes up in his car the next morning, it's to a taunt from Hyde that he won't need his wedding ring anymore. As Tom races home, terrified by what Hyde might have done to his family, he knows one thing. It's war between them.

A timely visit from a classic monster

Jekyll is a modern-day retelling of the Robert Louis Stevenson classic that brings one of the great monsters back to life. BBC America's four-episode series kicks off its American debut with a chilling two-hour premiere. Writer Steven Moffat has crafted a nightmarish thriller that lets us get to know Tom and his predicament before unleashing Hyde. It allows us to care about Tom and begin to see what he's up against as he desperately tries to hold onto and protect his family while battling the evil that lurks beneath his own skin.

Moffat seamlessly weaves Tom's struggle against Hyde with the mystery of the black van people, with Claire's confusion over why she's losing her husband and with Katherine's curiosity over Tom's past. And when Hyde finally bursts out, he is charming and terrifying and unpredictable. You are never certain what he might do next, but often it's not the expected.

The series is extremely well cast. However, Jekyll's success rests firmly with James Nesbitt, who is stunning in the dual role, going in an instant from loving family man to vicious monster. His Hyde acts on every desire he can, toying with Tom and pushing him to the breaking point. Nesbitt embraces the duality that is at the core of Stevenson's original story. Few actors could make these characters so different that they almost seem to be played by two different actors.

With three more episodes to go, Jekyll has a lot of story left to tell. Still, it's nice to know that this isn't some endless story that will continue as long as the ratings are good. Jekyll will have an ending, and that makes for great storytelling.