why is Marguerite (lady blackeney) so alone in lord Grenville s ball party??

At the ball, Lady Blakeney is paralyzed with anxiety, fearing for her brother's life because of the Chauvelin's revelation of the night before. She can't explain the situation to her husband, Percy, who she finds completely useless, and thus believes she must shoulder the situation alone. She follows two of the Englishmen and sees them hand-off a note. She follows the man who has the note to a room, where she distracts him long enough to read it just before he sets it to flame. The note says that the Scarlet Pimpernel will be in the supper room at one o'clock.