The Moon Is a Harsh Mistress
"The Cat Who Walks Through Walls" may be regarded as part of Heinlein's multiverse series, or as a sequel to both "The Number of the Beast" and "The Moon Is a Harsh Mistress." During a meeting of the Council of the Time Scouts, representatives from every major time line and setting written by Heinlein appear, including "Glory Road" and "Starship Troopers", and references are made to other authors' works as well.