It's a truism, more true in Hollywood than anywhere else, that the book is better than the movie.
Not, I'm finding frequently, when it comes to Zane Grey books.
"Mysterious Rider" was the rather generic title of Grey's book that was made as "Mark of the Avenger," also a rather generic title.
Again, Maurice Geraghty turned an excellent story into an even better screenplay, with enjoyable dialog moving along the exciting action.
Douglas Dumbrille as a cowboy ... I still am having some difficulty fully accepting it, but by gosh he was great! He was as at ease as any long-time cowboy star and thoroughly believable, because he was a star-quality actor, one of the best.
Sidney Toler, whom I had seen once recently in a similar best-pal role, still surprised me: He was perfect!
He and Dumbrille are just excellent actors, likable and believable in roles that are not what they were or became famous for. Excellent.
Russ Hayden is again a good-looking, likable, downright perfect cowboy, a fine actor in parts like this, and who should have become one of the biggest cowboy stars.
There are other superb actors, and some familiar cowboy faces, that make this an almost perfect movie, one I watched in a rather poor-quality print at YouTube, but which I would watch again.
There might be better prints around, and I hope you find one, but I really hope you get to see this excellent B western, well directed, well photographed motion picture that should leave you as it did me, thoroughly satisfied and ready for more.