In Chapter 31, what does Odile do when she thinks she is followed?

Odile takes books for Professor Cohen as she leaves the library just past seven p.m. She notices that the man in the tweed suit who has been coming to the library lately seems to be following her. She goes out of her way to lose him. At the Le Bristol, she opens the door and begs the concierge to let her out the back way. He does so. Odile is able to deliver the books to Professor Cohen.