How did Marguerite conclude that Sir Percy Blackney was the Scarlet Pimpernel

Lady Blakeney often questioned why her husband, a competent and thoughtful man, acted the fool. Needless to say, she never thought about figuring that out until she decided to snoop through his office one day, where she discovered a gold ring on the carpet in the room. The ring was engraved with a pimpernel, and Marguerite realized she been mistaken about her husband all along..... and that he was the Scarlet Pimpernel.