T. B. Smith, an Assistant Commissioner with Scotland Yard, briefly meets Superintendent Elk, the protagonist of his own series of novels by Wallace, with his rank sometimes varying, including Detective Sgt. and Inspector. Elk is in the CU, so this novel brings in T. B. Smith, who went on to appear in The Admirable Carfew, The Secret House, and Kate Plus Ten.
This crossover is one of hundreds covered in my book Crossovers Expanded: A Secret Chronology of the World Volume 3, which is to be published by Meteor House! Like its predecessors, this volume is an AUTHORIZED companion to Win Scott Eckert's Crossovers: A Secret Chronology of the World Volumes 1 and 2!