The Secret of Castle Doum

The Secret of Castle Doum
aka The Secret of the Locked Room
Het geheim van de Abandon Burcht (Dutch title)
The Secret of Castle Abandon (Dutch title, translated)

Written by Mike Butterworth
Illustrated by Don Lawrence

The Secret of Castle Doum was originally published in 9 instalments in issues 588 (21 April 1973) to 596 (16 June 1973) of Look and Learn magazine.

It is reprinted in Volume 10 of The Trigan Empire—The Collection (the Don Lawrence Collection).

It is reprinted in Volume 4 of The Rise and Fall of the Trigan Empire (Rebellion).