The moment I heard of a fire being lighted in Mrs. Inglethorp's room, I leaped to the conclusion that it was to destroy some important document ”possibly a will. 
I guessed that a fire was lit in Mrs. Inglethorp's room in order to destroy a document. 
mnli hypothesis: I guessed that a fire was lit in Mrs. Inglethorp's room in order to destroy a document.  premise: The moment I heard of a fire being lighted in Mrs. Inglethorp's room, I leaped to the conclusion that it was to destroy some important document ”possibly a will. 