S1, E7: Derek and Meredith try (unsuccessfully) to be discreet as they spend the night together at Meredith's house, but their haggard appearance speaks volumes to everyone - including Bailey, who warns Meredith to end the relationship. Meanwhile George suspects an anesthesiologist of drinking on the job but is reluctant to speak up about it, Alex treats a former schoolmate who finds honor in self-mutilation, Izzie's boyfriend takes extreme measures in order for them to spend more time together, and Cristina seems to be battling a case of the flu.