Episode 41 of The Trigan Empire
The Palace of Peril
aka The Glass Palace (the Collection)
Het complot (Dutch title)
The Conspiracy (Dutch title, translated)
The Palace of Peril was originally published in 2 installments in issues 611 (29 September 1973) to 612 (6 October 1973) of Look and Learn magazine.
It is reprinted in the Don Lawrence Collection Volume 10, The House of the Five Moons.