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 various series books exist within a common environment. The Lt. Heimrich series branched off from the Mr. and Mrs. North series. A retired academic who first collaborated with Heimrich on a case in Accent on Murder (1958) and again in Murder Can't Wait (1964)—a book that also introduced Nathan Shapiro and Merton Heimrich—returns to assist ADA Bernie Simmons in Twice Retired (1970).