To write an 'enigmatic return novel', you need to build suspense throughout the story. For example, when the character returns, don't reveal all their motives at once. Let the readers wonder why they are really back. Also, introduce some enigmatic side characters who seem to know more than they let on. They can drop hints and add to the overall mystery of the return.
One example could be 'The Return of the Native' by Thomas Hardy. It has an enigmatic quality as the characters' fates seem to be guided by both their own choices and some mysterious forces of nature and society.
I'm not sure as the name doesn't give much away about the characters. It could be a character who has been away for a long time and is now coming back, like a prodigal son or daughter.
I'm not sure specifically as I haven't read it. It could be about a mysterious return of a character or an event. Maybe it involves a character coming back to a place or a situation in an unexpected and puzzling way.
Rampaging Rats 2 was a 1989 sci-fi horror film directed by Damian Lee. The film was about a school professor who used a large number of animals for experiments in order to conduct hormone research, which caused some students to be dissatisfied. A student who loved animals broke into the professor's laboratory with the intention of destroying the experimental equipment, but was attacked by a group of rats that had grown larger after eating experimental hormones. This caused the entire city to fall into panic. It was not until the cause was found and the rats were eliminated that the war between humans and rats ended. The details of the movie's plot and cast were not yet available.