The Silent Invaders

From Author Wars - https://authorwars.com/publications/the-silent-invaders-47224.html

Overview:

Title: The Silent Invaders
Author: Robert Silverberg
Year: 1985
ISBN-10: 0812554604
Publisher: Tor
Price: $2.95
Pages: 216
Binding: Paperback
Type: Omnibus
Title Reference: Valley Beyond Time
Notes:
"First TOR printing: August 1985", no number line "Cover art by Tom Kidd", no visible signature Canadian ISBN 0-812-55461-2, Canadian price $3.50