La trama se basa en el robo de una fabulosa diadema de 39 berilos montados en oro, perteneciente a la casa real. La joya une a su incalculable valor material el hecho de ser una de las joyas mas famosas del tesoro real y uno de los bienes mas preciados del Imperio. La historia comienza cuando un distinguido caballero llega, sin avisar, al apartamento 221-B de Baker Street. Con aspecto alterado, se presenta como Alexander Holder, el socio de mas edad de Holder & Stevenson, una de las instituciones bancarias mas solidas y de mayor prestigio en el Londres de la epoca. Su relato nos traslada a su banco, donde un miembro de la familia real -sin decirlo, da a entender que puede tratarse del principe de Gales- solicita a Holder un prestamo de cincuenta mil libras durante unos dias, y en prueba de garantia ofrece la famosa diadema de berilos. -Una de las joyas mas preciadas del Imperio- exclama el cajero . La transaccion se efectua, y el banquero, para mayor seguridad, se lleva la joya a su casa donde, tras un incidente, desaparece una parte de la diadema, que contiene tres de las irremplazables piedras preciosas. Todo apunta al irresponsable y calavera hijo del banquero, que es encarcelado. Pero los berilos no aparecen y el banquero, desesperado, acude a casa de Sherlock Holmes. Tras una exhaustiva investigacion, Sherlock Holmes une las piezas del rompecabezas, encuentra a los verdaderos culpables (Su sobrina y su novio) y recupera los famosos berilos. La gran duda del relato es si para evitar el escandalo, teniendo en cuenta la importancia de las bailarinas implicadas, quedan libres de castigo los autores del delito. -Una persona que ha ahorrado a Inglaterra un gran escandalo publico- dice de Holmes el banquero al final del relato. A banker, Mr. Alexander Holder of Streatham, makes a loan of 50,000 to a socially prominent client, who leaves the Beryl Coronet - one of the most valuable public possessions in existence - as collateral. Holder feels that he must not leave this rare and precious piece of jewellery in his personal safe at the bank, and so he takes it home with him to lock it up there. He is awakened in the night by a noise, enters his dressing room, and is horrified to see his son Arthur with the coronet in his hands, apparently trying to bend it. Holder's niece Mary comes at the sound of all the shouting and, seeing the damaged coronet, faints dead away. Three beryls are missing from it. In a panic, Mr. Holder travels to see Holmes, who agrees to take the case. The case against Arthur seems rather damning, yet Holmes is not convinced of his guilt. Why has Arthur clammed up? Why is he refusing to give a statement of any kind? How could Arthur have broken the coronet (even Holmes, who has exceptionally strong hands, can't do it) and without making any noise? Could any other people in the household be involved, such as the servants, or Mary? Could some visitor, such as the maid's wooden-legged boyfriend, or Arthur's rakish friend Sir George Burnwell, have something to do with what happened to the coronet? The failure to resolve the case will result in Mr. Holder's dishonour, and a national scandal."