I'm trying to remember a science fiction novel I read as a child. I can remember the following details:
- The protagonist was a man had a Greek name, but was not ethnically Greek or even from Greece. IIRC in his timeline Grecian culture had taken over the world.
- The man was an agent of some kind.
- The agency had "vehicles" that could traverse timelines.
- Adjacent timelines were similar, but with slight differences.
- The vehicles could not move in space, only across timelines, though later in the story they developed vehicles which could move through both space and across timelines. These upgraded vehicles had a special name that I can't remember.
- The agency works with a species of aliens which can move across timelines on their own (their biology allows it).
- Their native timeline had a special designation. It was "Timeline 000" or something.
- These aliens later turn out to be antagonists.
Some additional minor story details that I can remember:
- At one point the man's communicator was either broken or malfunctioning, so he has to find or construct an AM radio to make contact with his handlers. The story was specific about AM radio.
- At one point the man and his female companion (IIRC they were not romantically involved at this time) were sent to a paradise planet called "Eden" and forbidden from wearing clothes there.