This is a detective novel, set mostly in Scotland in (I would guess) the early 1950s or even late 40s. I've read it many times before and always enjoy it - she's a very good writer and the plot is entertaining. But I'd never really noticed the homosexual subtext before.
On re-reading this time, it's surprisingly clear. The hero, Inspector Alan Grant, happens across a dead body on a train while going on holiday to Scotland. He becomes obsessed with the dead young man and decides to investigate the death, even though it appears to be an accident and even though it's completely outside his jurisdiction. He seems very taken with the young man's eyebrows for some reason

and at one point, while tussling with his own conscience, he says something like:
"You'll be developing a 'thing' for him if you're not careful."
"Don't worry - I already have!"
Later, the dead man's 'friend' turns up and helps Grant with his investigation, and it's even plainer that they were a good deal more than Just Good Friends. Nothing is said outright, and they both appear to have had girlfriends, but they worked for the same company, shared a house, borrowed each other's suitcases and even helped each other pack!!
Grant is a confirmed bachelor and the book ends with him exclaiming at the thought that he'd ever considered retiring from police work and getting married.
"What a ridiculous idea!"
Tey could hardly have made it plainer if she'd written Brideshead Revisited. At least imho.

I'd love to know if anyone else has ever read it and whether they thought the same thing....