The SS and Officers in Grandfather's Old House are very accurate with their weapons. If they hit you at all, you will suffer major Health loss. Whenever possible, try to take them out without letting them take any shots. It is possible to play the entire episode without ever losing Health points, (maximum is 110%).

Floor 1:

Make sure that you have acquired the HKMS-940 before entering the wood panelled area. 

Most of the human soldiers can be killed with the knife in doorways or corners. I was able to find both elevators while using a gun only once, on the officer who is behind a hanging skeleton.

I'm not convinced that there are twenty Secrets on this floor. I could find only 9, (including the corner in the grey stone area which doesn't open a secret area, not far to the left of the secret elevator). Anyway, if there are 11 more Secrets, they won't give you any additional Treasure or Weapons. 

There is a secret elevator on this floor, which brings you to floor 10.

Floor 10:

Avoid the urge to use your HKMS-940, or you may run low on Ammo for the next floor. The first group of Guards can all be killed with the Knife, if you are fast enough. Several of the Secrets are just pushwalls that don't reveal any Ammo, Treasure, or Weapons.

Floor 2:

I think there are supposed to be nine Secrets on this floor; I could only find eight. 

There are plenty of opportunities to use the Knife on this floor, but there seems to be an absolute limit to how much Ammo can be on the floor at any given time. In one area, I couldn't pick up Ammo from dead Officers, even when I used Ammo to kill them.

Some of the regular Guards can be killed by stabbing them around a corner, rather than face-to-face.

The only time I needed to use the HKMS-940 was in the room where five Officers were standing with their back to the door. 

There's plenty of Ammo and on this floor, so you won't need to be conservative.

Floor 3:

Almost everyone on this floor can be killed with the Knife, other than the Mutants and one room of SS near the elevator to floor 4. This includes all of the Guards at the start of the floor, if you sneak behind them and pick them off from just inside the door. Opening the secrets as you go will be helpful as many of the secret passages offer right angles at which multiple soldiers can be stabbed one at a time. Unfortunately, the number of kills on a given spot cannot be determined by walking through the completed floor.

Both Keys and the elevator are behind a secret area which comprises most of the floor. One of the secrets will block a doorway which, when open, will lead you through a small loop, if you are examining the perimeter for Secrets. 

Once again, I'm not convinced that there are 14 secrets on this floor, as I had 100% Kill and Treasure scores, but only 71% in Secrets,(10/14).

There are several instances on this floor where soldiers will open the doors on their own, so be careful where and when you save games.

There are three BJ life bubbles and two HKMS-940s among the Secrets. Many of the Secrets are heavily guarded.

Floor 4:

The soldiers aren't quite so stupid on this floor. They are often reluctant to leave their room to do battle with you. Firing a shot into the room will, however, usually bring them out.

Once again, I had 100% in Kill and Treasure score, but only 80% in Secrets, (I think it was 8/10). Perhaps there are additional Secrets when the game is not played at 'I am Death Incarnate'.

A gun must be used in the first two rooms, and you'll want to have a full Ammo compliment when you enter the Gold Key area.

Both Keys are in heavily guarded Secret areas. 

There are no Mutants on this floor.

Floor 5:

It is possible to complete this floor without having a shot fired at you, and only having to use a gun once, for the two Officers who are standing at the sinks in the red room connected to the Silver Key door. In many of the rooms, you can stab multiple soldiers around the corner of a door, before they can leave the room. I think I found 11/13 Secrets for the 84%.

Floor 6:

Other than the Mutants, and two Officers, (one behind a column, the other in a room with two mutants), everyone on this floor can be killed with the Knife. That strategy will involve a lot of luring soldiers out of rooms, and stabbing around tight corners at doorways. If you can see any part of a soldier's body as he comes out of a room, you can kill him with the Knife.

 Once again, I seem to have found all of the Secrets that contain Treasure, but, apparently, only 11/20 Secrets total.

Floor 7:

This is, by far, the most challenging floor to date, but all soldiers, (mostly Officers), can be killed with the Knife, until you enter the Silver Key door, where you'll find some Mutants. In fact, all human soldiers on this floor can be killed with the Knife. Quite a few Mutants guard the Gold Key. When you come to a spot where there are three doors from which to chose, take the one on your left. The center door also leads to the Gold Key, but it's much harder to kill the Mutants from that direction.

Load up on Ammo before opening any locked doors. In the first blue room after the Gold Key door, there is a spot where the wall is unstable. It's not a pushwall, more like an alcove. If you open the door next to this spot, and hide in there, you can stab all of the Officers and SS. It's as if they can't see you. They move around in front of you, but they don't shoot.

There are three BJ life bubbles, one out in the open, two behind pushwalls. 

There isn't a lot of Treasure on this floor. I think there are five Secrets. For once in this episode, I got 100% Treasure bonus.

Floor 8:

I learned something new on this floor. Some Mutants can be killed with the Knife, if you can get them as they exit a doorway.

Other than for Mutants, I needed to fire a gun twice, once for the German Shepherd behind the wall with pillars, and once more to attract the attention of a room full of Officers standing at attention. 

In one of the rooms of Officers, two are standing in front of sinks. The one at the far end of the room is semi deaf. He will not react to shouts, but may react to gunfire.

On this floor, and on some of the others, German Shepherds can inflict injury without exiting a room. 

Floor 9: 

All of the Guards and SS, and many of the Officers, can be killed with the Knife. This floor is quite challenging, particularly in the maze near the beginning, where you often encounter simultaneous attacks from opposite directions. The paths are relatively wide, and corners are short, so there are many places where a gun must be used. It is very possible to run out of Ammo on this floor if you fire indiscriminantly. All of the soldiers in the red room and beyond can be killed with the Knife, but it involves a lot of luring to distant spots. 

The Gold Key door, leading to the end of the episode, is in a secret area, guarded by Mutants, (don't try to kill them with the Knife).
Sometimes the Mutants behind the Gold Key door will emerge before you have obtained that key from the Boss. It may be dependent on where the next to last SS is killed.

I found the Boss to be a bit of a disappointment. I was able to dispatch him without having a shot fired at me. It may have been more difficult if I hadn't already killed all of the SS guarding him.
