The Door Into Summer

From Author Wars - https://authorwars.com/publications/the-door-into-summer-333954.html

Overview:

Title: The Door Into Summer
Author: Robert A. Heinlein
Year: 1983
ISBN-10: 0451123638
Publisher: Signet / New American Library
Price: $2.50
Pages: 159
Binding: Paperback
Type: Novel
Title Reference: The Door Into Summer
Notes:
18th printing as per number line. ISBN/price puts the year as 1983, most likely June The artist is not credited, the artwork is signed