Karate Masters vs the Invaders From Outer Space — Barbara Hambly

A novelette of 13,000 words in the Antryg Windrose series. Exiled wizard Antryg Windrose and his computer tech partner Joanna Sheraton lend a hand in making a low-budget martial-arts movie. But while filming in the Mojave Desert, it becomes obvious that someone or something from another dimension is out to kill off everybody in the project. Antryg must use all his powers to figure out what's behind this and who is really the target of the attack - BEFORE his own dojo-mates panic and decide he's to blame.