In Book Club, an amiably dim-witted 2018 comedy, four women of a certain age were inspired to revolutionise their sex lives following close readings of that timeless literary classic, Fifty Shades of Grey. The film was only made bearable by the ensemble charm of its stars — Diane Keaton, Jane Fonda, Mary Steenburgen and Candice Bergen — and they’re at it again in Book Club: The Next Chapter.