The Door Into Summer

From Author Wars - https://authorwars.com/publications/the-door-into-summer-401489.html

Overview:

Title: The Door Into Summer
Author: Robert A. Heinlein
Year: Unknown
Publisher: Signet
Price: $1.25
Pages: 159
Binding: Paperback
Type: Novel
Title Reference: The Door Into Summer
Notes: 12th printing as per number line.
Also appears in the Ace box set "Robert A. Heinlein: Beyond Time and Space With the Master of Science Fiction".