HOW DO I DEFEAT THE COLONEL AND HIS MEN?

You don't need to worry about his men. Calvin, Adam and the parrot are more than capable to deal with them.

You just need to get the brave Colonel out of his hidey hole.

Good thing the people who installed the panic room weren't particularly good at their job. Read the notice that shouldn't be there.

Where is the rear of the unit?

There's a map somewhere if you need to orient yourself.

Actually, the map is exactly at the rear of the unit.

Now, what could the password be?

The Colonel said he set it himself.

You might find a clue in his room.

Read the memo in the safe.

The keypad has numbers only, so what in the memo could be expressed in numbers?

How about a date?

If you don't know when Boxing Date is, there's a calendar in the staff dining room.

(SOLUTION FOLLOWS)

↓

Press 1-2-2-6

Now go back to the Colonel to see what happened.

You can now finally take the dagger to Jackson to show him what you're made of.

Don't forget to talk to him about the Duke too. In all this commotion, his little reveal almost slipped your mind, didn't it?