The movie follows Conan as he escorts a princess to find a key then horn for a sorceress who hopes to bring her demon god to earth. He works to help her (ignorant of her final motives) as she has promised to return his love from the first movie should he help her. The film has much more of a quest feel to it than the first which was simply a revenge and origin story. In the end, Conan frees another kingdom from an evil despot and sets off on his own once more. Theoretically there would have been a third Conan film to finish his story, but it never happened.
Conan the Destroyer is not a movie that one needs to see, however I own it because it came with Conan the Conqueror, I like to be complete in my series ownership, and I like Arnold movies. Check it out if you haven't seen it.
1. His thieving sidekick seems to have been replaced by a white guy. In Conan the Barbarian he was played by a Latino or possibly Filipino... Though it's not the same character, it is interesting they replaced him with a character who is almost entirely the same, but white.