Michelle Ryan, known for her long-running role as Zoe Slater in the soap opera "EastEnders", was revealed by tabloid newspaper "The Sun" to have been cast as "Jekyll's sultry assistant" (Katherine Reimer) in August 2006. Ryan believed herself to be too young for the part, though that aspect had already been written into the character. To prepare, she consulted the Royal College of Psychiatry. Ryan dyed her hair red for the role to help differentiate her from Tom Jackman's wife. Denis Lawson was cast as Peter Syme. The actor consulted his post-graduate son for information on Syme's job.