Pick up the emerald. The point at which you start is marked with a green dot. After killing all the enemies in the nearby corridors, the gatekeeper should attack you (he's normally by the windlass), who will leave behind a key which opens the crate marked with a yellow dot. The stairs leading to the upper floor are marked with a black dot. The red one is for a windlass (on the upper floor) which will lower the bridge and create a path for the Inquisitor. Return to the crate at the yellow dot, open it and talk with Ursegor (white dot).
The search for the map
Brent will suggest you find a map of the temple. He'll send you to Jorgensen, who's in the deeper parts of the temple. Go through the passage at Brent's left hand and further - down the path marked by the mushrooms. At your left you should find a runesword and further - Jorgensen who will tell you to follow a nearby path.
Turn right at the intersection (violet lights). At the end of the corridor you will come across a group of enemies. One of them will drop a key to the cell. Go outside and follow the path. On your way you will encounter among others, an Ashbeast (red dot).
After getting to Jasmin's house, try to save the people there. At one of the bodies you will find a map of the temple from which you have just left. Return to Brent.
The opening to the crypt
Mendoza will send you for Vince. Once he goes to the Inquisitor, you will be able to read the text carved into the column.
Free the ghost of Ursegor
Ursegor will send you in search of his subordinates, possessing specific crystals. Take the golden bust and return to the corridor in which the Inquisitor is at the moment.
Begin from placing the bust on the pedestal in the room marked with the black dot. Inside you will come across Zul Utur. At his body you will find some inferno and conjure skeleton spells, a sapphire, his skull ant the crystal you need. Take the bust back while going out of the room.
The room marked with the red dot will lead you to a Zel Zeret, a tougher version of the Ashbeast. Remember about searching its body.
The last enemy, called Zal Zaran, is waiting in the room marked with the yellow dot. Take his weapon (titan sword), skull and the crystal. Return to Ursegor and free his spirit. Open the sarcophagus and take Ursegor's skull.
The titan trap
You have to open the big gate in front of the corridor leading to Ursegora. Find the four pedestals and place the skulls in the order seen above.
After opening the door, things will get quite messy. Defeat you former allies and listen to what Ursegor has to say.