Iobel doesn't break stride. She shuts her eyes to hide the white glow of a charging spell, and when the forty-one seconds this particular spell takes are up -

the guard following her falls unconscious unceremoniously. He'll have a nasty headache all day tomorrow.

Iobel breaks into a run, and charges up another of the same, ready to abandon it if the closet's unguarded but suspecting that it's not.