Crown Witness - Tapa dura

Detective heroine Nell Bray once again finds herself in the midst of a mystery as she and her fellow suffragettes organize a procession. The movement has decided to take advantage of the cheery atmosphere surrounding George V's coronation to promote their cause with a peaceful five-mile-long march culminating in a rally at the Royal Albert Hall.
All goes well until Nell spots an unusual float at the tail end of the procession. As she and her hapless friend Simon Frater move in to investigate, a fire breaks out on the float, confusion follows, and a shot is heard. When the crowd clears, Simon is left holding the gun and examining the body of the victim as the real suspects escape.