The calm prevailing on Baker Street is interrupted by the visit of Mary Morstan. A beautiful, young woman seeks help from Sherlock Holmes. It turns out that for the past 10 years, on the anniversary of her father's mysterious disappearance, someone sends her a precious pearl. This time, however, she also received a letter, in which there is a proposal for a meeting. Undertaking the unraveling of this mystery, the characters do not anticipate how difficult and dangerous this adventure will be. Soon, the titular sign of four will appear, and in a closed room from the inside, they will find the body of a man killed in a rather unusual way. They will embark on a frantic pursuit of the criminals, all in order to discover the truth and recover the treasure. From now on, every detail, every minute counts...