Lockridge's various series books take place in a shared universe. The Lt. Heimrich series was a spin-off of the Mr. and Mrs. North series. A retired college professor who first assists Heimrich with a case in Accent on Murder (1958) and again in Murder Can't Wait (1964)—a book that also features the meeting of Nathan Shapiro and Merton Heimrich—shows up to help ADA Bernie Simmons in Twice Retired (1970).
Lockridge's series novels share a common setting. The Lt. Heimrich series diverged from the Mr. and Mrs. North series. A retired educator who initially worked with Heimrich on a case in Accent on Murder (1958) and again in Murder Can't Wait (1964)—a book that also featured the collaboration of Nathan Shapiro and Merton Heimrich—reappears to help ADA Bernie Simmons in Twice Retired (1970).