Episode 57 of The Trigan Empire
The Lost Valley
aka The Nobes
De vergeten vallei (Dutch title)
The Forgotten Valley (Dutch title, translated)
Written by Mike Butterworth
Illustrated by Don Lawrence
The Lost Valley was originally published in 8 instalments in issues 740 (20 March 1976) to 747 (8 May 1976) of Look and Learn magazine.
It is reprinted in Volume 12 of The Trigan Empire—The Collection (the Don Lawrence Collection).
It is reprinted in Volume 5 of The Rise and Fall of the Trigan Empire (Rebellion).
Plot summary (Dutch)
MediaFire via British Comics Compilations