Showing By the Light of the Moon by Dean Koontz

When Dylan O'Conner, together with his autistic brother, Shepherd, pulls into a motel off the interstate highway, all he wants is a good night's sleep. Yet within the hour he finds himself bound, gagged and being injected with a mysterious fluid by a lunatic doctor, who claims Dylan will be the carrier of 'his life's work'. Comedian Jillian Jackson is midway through a tour of seedy venues, accompanied by her pet pot-plant Fred. But her plans for stardom are dramatically altered when she too falls victim to the eccentric scientist. The doctor warns his victims that he is being pursued and that they too are now targets. If they are caught, they will be killed. Both are sceptical. Before long, they are beginning to wonder if the lunatic doctor wasn't quite so mad after all.