Sam Casey is an agent for INTERSECT, a government think tank and operations center that specializes in covert missions. During a diving assignment, Sam is struck by the radiation from an underwater explosion. The radiation makes him invisible and INTERSECT devises a way to make him visible again by means of a computer-controlled watch. However, he can disable this and become invisible for a short time. However, if he does this for more than 15 minutes within a 24 hour period, he will die. This ability to become invisible makes him a very effective secret agent.