The boys help out a school-friend, Diego Alvaro and stumble across a centuries old mystery, involving a missing, jewel encrusted sword, encountering bush-fire, sinister cowboys and savage dogs along the way. Briskly told and very well constructed, as with all Arden stories, this suffered for me in that the location - which was key - had to be explained at length and it felt dry and uninvolving. It also hinges on the fact that the mystery is solved, essentially, by the weather, with mudslides showing the way. There was a lot to like - especially that the boys are helped out by Prof Marcus Moriarty, a nice link back to the Sherlock Holmes connections of the earlier Arthur-written books - and the atmosphere is good (especially the rain and chill in the air), but I found myself distracted and unable to picture the scene properly for a lot of the outdoor stuff. Recommended, nonetheless, but not prime Arden.