3.Why had Mr Douglas changed into his dressing gown and left his gun, although he never went anywhere without it?

Mr. Douglass was ready to retire... to go to sleep. He kept his gun in his pocket, and his dressing gown did not have pockets.

But, by bad luck, he was in his dressing gown and had left it in the bedroom last night. Once the bridge was up, I guess he thought he was safe.”