Published 1933
Written by Sydney Thompson & George V. Denny Jr.
Published by Samuel French
Format: small book
Original price: 50 cents

From the introduction:
"The purpose of the game is to provide theatrical entertainment for clubs or drawing-rooms in which the audience shall take the part of witnesses of an event being enacted before them. After the performance the audience will be cross examined on what they have observed and will be asked to solve the mystery."

User summary:
Detecto-Plays contains 6 short plays that are intended to be fleshed out by a small cast. At the end the audience will be asked by the director ten questions. Each question that is answered correctly is worth 10 points. Wrong or incomplete answers are worth nothing. Some of them are single scenes plays, some have as many as six scenes.

This appears to be a very early version of modern murder-mystery party games. It's unusual in that the scenarios and dialogs were written by two playwrights that were producing work for New York theatres at the time.

One of the scenarios also includes a game within the game as the actors play a game called "murder" which appears to be a popular party game at the time, similar to "Are you a werewolf?"