Relocating from Canada to UK, what should I do?

My father was British, but I spent most of my time in States and in Canada, farming there. Then one day I found out that my British uncle Charles died and left his estate in Devonshire to me. I came to Britain to take a possession of it. Upon arrival, I was met by a Dr. Mortimer, a friend of my late uncle's, who lived near the estate. We spent a day, shopping in London. The next morning I received a strange letter, made up from the words, cut out of a newspaper, which said: "As you value your life or your reason keep away from the moor." (My new estate is on the edge of a large moor). Then I found out that one of my boots disappeared (I put them out at the hotel's door, to have them varnished, and there was only one boot there in the morning!). I could get no sense out of the chap who cleaned them. Then Dr Mortimer took me to a chap, a PI, and they both told me a long story about a curse and all the heirs dying violent death and so on. I don't know much of British life yet, so I am not sure what's going on. Is this normal? Is this letter a joke, or someone wants to keep me away from my new inheritance? Who'd want my boot, and one boot only? Can I trust Dr Mortimer and that detective chap? And what should I do?