From the back cover (translated from Dutch):
Duistere Catacomben is an expansion for 'Schimmen en Schaduwen'.
Duistere Catacomben contains a couple of new monsters, rules for creating 'constructs' (magical, metal creatures), sixteen ready-to-play NPCs, and finally paper cut-out figures to be used as miniatures.
Furthermore, 3 adventures are included:
Tool of the Devil: A group of refugees asks the heroes for help. An army of orcs has driven them from their village, but there's more to it than initially suspected.
Word of Truth: The heroes have to recover a dangerous spell from a ruin. When they finally get to the spell, they are faced with a dilemma.
Buried alive: Umbert, son of the local baker, is buried alive. When saved, he tells the strangest stories that soon become reality.