Three worlds - blasted, hi-tech, magic

Question

I originally read this in the 1980s or 1990s; the author was considered up-and-coming at the time, but not really well-known.

The two main characters were a 'courier' and a wealthy student:

• the 'courier' wasn't a messenger so much as an escort into the 'hidden worlds'. The hidden worlds were only accessible through a tunnel on the blasted world; this led to a world of high-tech that was treated as magic; from there, there was another tunnel to a world of real magic (by invoking sprites/imps/demons/etc).

• the wealthy student was ostensibly studying the hidden worlds, her real purpose was to study the courier/escort. She was also trying to get away from a smothering bodyguard, who managed to follow them into the hidden worlds.

The denouement involved a revelation that there was a fourth world, where the demons invoked on the third actually came from, and there was a subplot involving a character trying to bring a demon into the high-tech world.

Answer 1

This looks like Triplet by Tim Zahn.

The main characters are a researcher (Danae) and an escort (Ravagin) who are entering through gateways into alternate versions of a world.

Danae is nominally studying the words but actually studying the impact of travelling between worlds (and being in the alternate worlds) on the escorts.

The bodyguard (set on her by her father) is there as well as the hidden high tech and the demons.