The BBC television movie, which I've only been able to find online, is a decent version. The story involves twins, and Mark Greenstreet plays Brat and his supposed twin, Simon.
*Spoilers*
The one place the movie falters is at the end. In the movie, Brat ends up with the supposed sister who is really his distant cousin. Movie Brat also comes across as far more aggressive and confident than his book self.
In the book, Brat is far more like the dead boy, Patrick. After a lifetime surviving alone, he is self-contained and wary. He is also fundamentally moral and sensitive and pursues the mystery to a dangerous end. He also, like everyone else in the family, adores horses. He finds his strident, overly confident cousin (who originally thought she was his sister) attractive--but not ultimately what he wants.
His eyes came away from the ceiling, and watched her. She saw his fingers being to play with the sheet, unhappily.
"Are you going away to Ulster, then?" he asked.
"Only if you will come with me, and run the stable for me."
The easy tears of the newly-convalescent rose in his eyes and ran down his cheek.
"Oh, Bee!" he said.
"I take it means that my offer is accepted," she said.
Tey does not indicate whether the relationship is a romance, friendship, partnership, or all the foregoing. Aunt Bee is the age she is portrayed in the movie where she is played perfectly by Angela Browne. Older than Brat by about a decade, they fall well within the range for a possible match. And easy comradeship is plausible, no matter what the relationship's label. It's a wonderful ending, and the ending I would have rooted for with the movie.
