The leaking window

An original fiction passage set in the nineteenth century.

Rainwater was spreading across the museum gallery floor, towards two piles of catalogues. Clara lifted the catalogues onto a chair and slid a brass bowl beneath the steady drip. A flash of lightning revealed a thin crack running across the window above her. She summoned the porter, then stood in the doorway to prevent visitors entering the gallery.

Give two things Clara does before the flash of lightning.