A great deal of things were happening at once:

1. The pair were caught.
   
2. Miss Gallivan fired a jinx at the woman who had caught them, sending her swooning to the floor.
   
3. The trouser situation.

Fitz did not think museum openings were typically so eventful, nor debutantes so...ready with a spell to thwart would-be ruin. In spite of Miss Gallivan's instruction for him to leave, Fitz was filled very much with a desire to stay and to watch how this rather unbelievable chain of events came to a conclusion. It was, however, her reputation on the line—even if this was merely muggle society—and today would not be the day he would face down death or the vicar.

With one last look at the girl, his expression a mixture of disbelief and impressed, Fitz disapparated from the scene like a thief in the night.