Everyone loves a wedding... and a family row. Three sisters from very different walks of life return to their childhood home to celebrate a momentous event: the third wedding of their twice-widowed mother, Diana. As the weekend unfolds in unexpected ways, Katherine, a Captain in the Royal Navy; Victoria, a Hollywood star; and Georgina, a palliative nurse, are forced to reassess their childhood - and make tough choices of their own.
In My Mother's Wedding, Captain Katherine Frost (Scarlett Johansson) of the Royal Navy is about to embark on a new command when she finds herself reflecting on her childhood and her late father, John Frost, a Navy pilot. As she reads emails, her younger sister, Victoria (Sienna Miller), a famous actress, gives a live interview on a glitzy talk show where she publicly discusses her family's tragic past, primarily the loss of her father during the Falklands War and her mother's subsequent marriage to his best friend, Johnny Monson, who later went missing in action.
The three sisters reunite at their childhood home in Hampshire ahead of their mother Diana's (Kristin Scott Thomas) third wedding to the amusingly named Geoff Loveglove (James Fleet). Tensions arise as they navigate personal issues, including Victoria's romantic pursuits, Georgina's (Emily Beecham) concerns about her husband's fidelity, and Katherine's unresolved feelings for her partner, Jack.
As the wedding day unfolds, long-buried family secrets are revealed, causing rifts between the sisters. Amidst the chaos, Katherine receives unexpected news from Jack, which challenges her plans and priorities.
