Try getting the key from Lanilor's house anyway, after defeating the black ring member. If that doesn't trigger the proper speech options, try standing inside Mardaneous' house and closing the door, to trigger his 'help, I'm locked in' expression he would have said clicking on the locked door from outside.
There is no key to get further in the catacombs. You need to collect 3 orbs from around the first level (
map) and drop them on the pentagrams beside the locked door to the stairs down. A nearby book should describe this. The grave will be opened after you get past the locked door and take the stairs up. In the graphics options change the darkness setting to 50 and increase the gamma to help see better at night or underground.
A hex editor is a program for editing binary files, similar to a text editor for text files.
