Chell knew the station better than almost anyone by now, but finding her quarry would still be next to impossible without Hypatia's many eyes.

(Sometimes, when she passed a camera, she had the strangest urge to pop a portal under it and knock it off the wall. She could never remember why.)

As soon as she receives the coordinates where he was last sighted, she's on her way, flinging from building to building to speed her passage.