You can not enter the mansion by the front door. The passage is blocked by a bomb.

Enter through the side door, the kitchen entrance.

Fight the guards in the kitchen area and in the adjacent hallway.

Then take on the enemies in the dining room. Get the plasma gun from the Super SS.

Find a cross in the sitting room.

Find extra plasma ammo in the vine cellar. Watch out for the enemies hiding among the shelves.

Enter the central hallways. Use your plasma gun to kill the Super Officers around the corner and the Super SS behind the mirror. Find health chalices by the purple monster.

Bring down the guards in this living room for more reinforcements.

Continue.