Mrs. Inglethorp is out, and he sits down to write to his accomplice, who, he fears, may be in a panic at the nonsuccess of their plan. 
Mrs. Inglethorp is inside, and he is not writing to his accomplice.
mnli hypothesis: Mrs. Inglethorp is inside, and he is not writing to his accomplice. premise: Mrs. Inglethorp is out, and he sits down to write to his accomplice, who, he fears, may be in a panic at the nonsuccess of their plan. 