Clary can kick demon butt when she really wants to. She's good at it. What's she's not good at is partying all night and then dealing with the hangover. Having used a rune to get rid of her headache, she'd stumbled free of her apartment searching for coffee. And sugar. So much sugar.

So it's at the coffee store that she literally bumps into him, her shoulder connecting with his ... arm. She's short, sorry.

"Ah, oops." And then getting a look at him, "Isaac?"