The Howling III rewrites the history of the previous books slightly, bringing the events forwards to the mid-80's, but the werewolves of Drago remain.
This time, the story moves to the areas surrounding the original village, and the finding of a strange boy who is savage and yet, vulnerable.
He is adopted by carnival folk and made into an attraction, until others who understand him come looking for him, bringing the cycle of blood, sex and death to it's climactic conclusion.
This is definitely a weak sequel to the original novel - and as yet, has not been adapted into one of the movies - though slight elements from it made it's way into the 6th Howling movie - The Freaks.
Brandner, by now, was probably working on the sequel to the Howling film - and probably wish he hadn't, and as such, the third book seems somewhat stilted, with a "We've seen this all before" element to it, which ultimately disappoints in a way the films didn't - probably because they moved away to different areas with each sequel - at least up until the abomination that was the Howling VII.
By now though, if you've seen any of the films or read the two previous books, you'll know what to expect, and whilst competently written, lacks any of the thrills and titillations of the original book, and less of the horror and rage of the second book.
I think though that the Howling in book form had run it's natural course, and though a weak end to the trilogy, Echoes, the third and final Howling novel at least provides some moments of horror.