The Mastertronic re-release has two bugs that prevent you from completing the game. The first problem is that when you come across the silver dagger in the desk and try to take it, you're told that you can't see the silver dagger. The other problem is that when you ask Eva to kill the Darg-Vool, she refuses to do it for you, despite the fact that this is the only way past that particular problem. A patch was provided by Chris Jones in Your Sinclair issue 22, page 84, with further corrections provided by Battle Bunny (JimG) at The Tipshop.
The original release of the game is OK and doesn't have these bugs.