On the brink of leaving for a mission abroad, David Vincent, consultant, locks himself out of his home in the middle of the night. He is obliged to ring at Rose's door, a neighbor on his landing, the only one to be still awake at the that time of night. But the insecurity reigns and after all, who prooves to her that David is really her neighbor? After a tight interrogation, Rose is finally convinced and accepts that he calls a locksmith from he flat. While he phones, Rose realizes that this anonymous neighbor is not a stranger.