The whole case had sounded fishy from the beginning. Why would an amnesia victim go to a detective when he needed a doctor?
But Ellery investigated and soon discovered why they needed him. Howard Van Horn and his beautiful stepmother were being blackmailed for adultery. It was an ugly situation.
Then it exploded into murder!
Ellery solved the case in record time. But suddenly. while he was accepting everyone's praise, he realized he had made a horrible mistake.(Cover)

A Triangle for Murder

These are the people who formed the triangle:
Howard Van Horn -- a young sculptor suffering from strange attacks of amnesia. He goes in desperation to Ellery Queen with a baffling problem.
Diedrich Van Horn -- Howard's millionaire foster father. His money bought him a wife tailor-made to his specifications. He needed Ellery Queen too -- but for a more sinister reason.
Sally -- the young and beautiful wife. She came from the wrong side of the tracks but moved in the Van Horn mansion with complete assurance.
Ellery Queen finds a pattern of sins that leads irrevocably to murder.

Ellery is persuaded to accompany an old friend to his ancestral home when the latter arrives at Ellery's house covered in blood and unable to remember anything from the past few weeks. There, tensions erupt and foul play results in the murder of one of the household's members.

One of the first Queen's I read and it immediately reminded me of a 'Ten Little Indians' setting. Which at the time wasn't that difficult because Agatha Christie was much more popular at the time. The thing that struck me most was the fair-play. Christie's detectives always found some hidden clue only they themselves had noticed whereas Queen gives you 'a shot' at the solution. Another trip to Wrightsville, the first of the self-doubting tales, and another double-twist ending. Brilliant portrayals.  Movie: "Ten Days' Wonder".

Ten Days' Wonder Translations:  Danish: Ti dages frist  Dutch/Flemish: De Tiende Dag  (aka De Tiendagsvlieg)  Finnish: Kymmenes rikos  French: La Decade Prodigieuse  German: Der Zehnte Tag (aka Am Zehnten Tag)  Italian: Dieci giorni di dubbio (aka Dieci incredibili giorni)  Japanese: tookakannofusigi  Norwegian: Ti dagers underverk  Polish: Zázrak trvá devět dnů  Portuguese: Dez Dias de Misterio  aka Un Misterio De Diez Dias) Romanian: Minunea de zece zile  Russian: ЧУДО ДЕСЯТИ ДНЕЙ  Spanish: La maravilla de los diez dias  aka La década prodigiosa Swedish: Tio dagars underverk  Tjech: Drama desatera dní