The central character was Horatio Black, better known as Boston Blackie, a former criminal who had become a detective. His girlfriend, Mary Wesley, helped him to solve crimes before the police could do so.
Kent Taylor portrayed Blackie, and
Lois Collier (selected over 60 other actresses who sought the part) played Mary. The couple was usually accompanied by a dog, Whitey. Mary was a nurse who was "very independent and gutsy".
Frank Orth played Inspector Faraday, a "typical not-so-bright police detective". Episodes included many wisecracks. Actors who often appeared in supporting roles included
John Doucette,
John Eldredge,
Herb Vigran, and
Ben Welden. Tom Hanlon appeared midway through each episode to introduce the commercial break. ==Production==