In The Sign of Four, Mary Morstan arrives at 221B Baker Street begging Sherlock Holmes for help in finding her missing father, along with unraveling who is sending her unidentified gifts of pearls along with a letter asking her to meet someone unknown that night. Holmes accepts the challenge presented by this very unusual mystery. He and Watson are off to find the missing fortune and the criminals behind these strange doings that by twists and turns turn into a murderous treasure hunt.