Parisian couple Simon and Hélène Sandberg are relieved to find a trustworthy buyer for the basement they own in their apartment building. It is only after they sign the deed, however, that the true identity of the lonesome man in need of some storage space is revealed to them – not the kind, former high school history teacher they initially thought, but a Holocaust denier who spreads his distorted views and lies on the internet. His presence in the basement in which Simon’s relatives once hid from the Nazis disrupts the life of the couple and their teenage daughter and forces them to confront their own feelings about Simon’s Jewish identity – and those of their ostensibly liberal non-Jewish neighbours.