This illustrated novel takes place during the first 1968 Apes movie, filling in the story that we did not see on screen. It answers all of the unanswered questions and continuity problems presented in these films. For example, we're given the reason why Taylor's spaceship, , Liberty 1, crashed onto the future earth (it hit an identical Liberty 1 in the time-stream, presumably the craft manned by Cornelius, Milo and Zira in ESCAPE FROM THE PLANET OF THE APES). The major human in this novel is astronaut Landon, who eventually gets lobotomized by Zaius in the first movie. So, what led to this? After all, he was another intelligent human.
For some reason can't speak around the apes. He at first attributes this to the strange fruit he ate with the feral humans, just before the gorillas attacked him and his friends. But it's really because of the telepathic mutants from the Forbidden Zone, who are controlling him to a certain extent. They were very aware of the three astronauts crashing in the lake. While General Ursus dominates BENEATH as the main "bad ape", here we're given Chief Security Marcus, a much more complicated primate.
In flashback scene with Landon we're introduced to Jonesy and Brett, who would make the trip in the film's sequel, BENEATH THE PLANET OF THE APES. And we're given a glimpse of Landon's frustrating life, from the difficulties he has with his marriage and his ever disappointed wife, to a previous space mission to Jupiter during which he started an affair with Stewart (She had died when her cryonic bed cracked, causing her to age).
What I like about this book is that it adheres to the Apes mythos and incorporates some other things, such as Taylor leaving behind a daughter (who, in the Adventure Comics POTA comic series would grow up to follow in her father's footsteps). It addresses a lot of the questions unanswered in the first ape movie, such as how did those three chimps manage to fly Taylor's spaceship back to Earth in the time stream?
The book is also heavily illustrated by such artists as Matt Busch, Joe Jusko and Jim Steranko, which reminds me of Marvel's old PLANET OF THE APES magazine covers.
CONSPIRACY OF THE PLANET OF THE APES is highly recommended. It's one of the best APES tie-in books I have ever read.