Essentially enjoyable as usual.
This one's not bad, but not one of Francis' best. It uses the same tropes as usual - strong male lead who has some connection with horses and some fatal flaw (this case bad lungs and vision) teaches us about an odd world that we're not familiar with (in this case Russia.) He battles some nasty vicious people in a collection of random attacks (getting more hurt during each attack) until Superior Observation allows them to Put All The Parts Together.
The Russian/Cold war aspect seems to have dated worse than a lot of his other works. Ah well.