Cait – from Time Out Bookstore – gave us her a list of standalone mysteries.
They are really clever puzzles with very satisfying endings.
The Song of Seven

by Tonke Dragt
The Westing Game

by Ellen Raskin
York

by Laura Ruby
Clementine Loves Red

by Krystyna Boglar
From the Mixed Up Files of Mrs. Basil E. Frankweiler

by E.L. Konigsburg