David Renwick wanted to write a detective series that dealt with the actual work of detection rather than action, which most crime dramas appeared to focus on at the time. Also, whereas most of these were about "who did it" ("Inspector Morse" or "Taggart") and "why it was done" ("Cracker"), this new series would be about "how it was done", with such tropes as murders committed in locked rooms, a person being in two places at once or impossible thefts. Finding a culprit would still be part of the detective's job, but the emphasis would be on discovering how the crime was committed.