Straight never coalesced for me. Hero Derek Franklin is trying to solve various questions left open by the sudden death of his brother. It had all the elements of a Francis novel, but the parts of the mystery felt random, even after it was all solved. Perhaps this is because two separate mysteries collided, that of the missing diamonds and that of the mysterious performance of the horse Dozen Roses; also, Greville was fond of weird gadgets, and Derek has to figure out some of those, as well. I might have liked the novel better had these things all turned out to be linked in some way other than that all were things left open by Greville's death.
Also, three different "specialties" were crammed into this one novel: the hero is a jockey near the end of his career, who's recovering from a broken ankle, and tells us about being a jockey and thinks about how his life will be when he becomes a trainer; his dead brother Greville was an importer and seller of semi-precious stones; and Greville had a liking for weird gadgets. These three things were all interesting, but didn't coalesce into a comprehensive picture.
The love interest isn't really a love interest, and that would be okay, but the part with Clarissa felt tacked on; she wasn't really needed, and didn't make a huge change in the hero's life. June, who worked in Greville's office, felt like a nascent love story that Francis just didn't feel like writing.
However, one thing in Straight felt strong and true, and that was the death of Greville at the beginning of the book and the moments throughout when Derek and, later, Clarissa, are dealing with grief. For me, that's a reason for reading this. The rest, well, there are plenty of other Francis novels that are a lot better.