As Doug McLeod (David Tennant) and his wife Abi (Rosamund Pike) set out on a challenging adventure to celebrate Doug's father Gordie (Billy Connolly)'s 75th birthday in the breathtaking Scottish Highlands, the heaviness of their tumultuous past weighs down upon them like a dense fog. The tension between them is unmistakable, reverberating from their recent separation caused by Doug's infidelity. Although they have reunited for the sake of Gordie, the fragility of their relationship lingers in the air.
While battling through congested roads to transport their three children—Lottie (Emilia Jones), Mickey (Bobby Smalldridge), and Jess (Harriet Turnbull)—the family finds it increasingly difficult to leave their troubles behind. Lottie, struggling to trust her parents due to the recent turmoil, is forced to confront the web of lies that has entangled their lives.
Upon their arrival at Gavin McLeod (Ben Miller)'s opulent mansion, an uncomfortable atmosphere prevails as Doug and Gavin engage in a subtle, yet fierce, competition for dominance. In the midst of it all, Gordie, despite the shadow of terminal illness hanging over him, maintains a playful spirit, urging his grandchildren to embrace life and shed their worries.
As preparations for the party continue, Gordie takes the children on an unexpected escapade to the beach, sharing that he has Viking ancestry. This revelation ignites Mickey's imagination, while Gordie expresses his wish to be cremated and scattered at sea to prevent any disputes between Doug and Gavin after his passing.
Tragedy strikes unexpectedly when Gordie passes away peacefully. In a heart-wrenching moment, Lottie is left to inform her stunned family of the heartbreaking news. Instead of grieving openly, she retreats to the beach, where she finds her siblings grappling with their grandfather's loss. Overwhelmed by a profound sense of respect for Gordie's wishes, the three children construct a makeshift raft from their grandfather's truck and send him off ablaze into the sea—a heart-rending tribute that mirrors Viking traditions.
As the flames engulf the raft, it becomes clear that Gordie's departure has formed an unexpected bond within the family, their sorrow tempered by a newfound appreciation for life. Meanwhile, the bewildered adults are left to process a string of extraordinary events. Doug and Gavin take a poignant trip to the beach, where they are met with a sobering sight: Gordie's beloved pick-up truck partially overtaken by the merciless tide. In that moment, Gavin, overwhelmed by the weight of their shared grief, collapses in Doug's arms. Simultaneously, Abi and Margaret must face the task of breaking the devastating news to the assembled guests, who transition from shock to outrage.
In the aftermath, social services worker Agnes Chisholm (Celia Imrie) arrives to investigate the children's conduct. Lottie's honest reflections stir Agnes to consider removing the children from Doug and Abi's custody. Meanwhile, the media hastily sensationalizes the incident, presenting the children in an unsympathetic light.
Amid this upheaval, Mickey and Jess accidentally discover a video that will forever change their perspective on Gavin and Margaret's relationship. The candid footage reveals Margaret's vulnerability as she lashes out at a fellow shopper—an eye-opening moment that underscores the challenges that can afflict even the most picture-perfect families. This shocking revelation triggers a wave of introspection within the household, as Doug and Abi implore the public to understand their children's actions in a more compassionate light.
As the tide of public sentiment gradually shifts in their favor, Agnes ultimately concludes her investigation, allowing the children to remain under their parents' care. In a poignant climax, Doug and Gavin, having set aside their previous animosity, come together to honor the memory of their beloved Gordie. Abi expresses her determination to keep her family rooted in their current home rather than uprooting them to Newcastle, paving the way for a civil divorce. As the credits roll, the extended family converges on a hill overlooking the beach, commemorating Gordie's legacy, and in a joyous display of togetherness and laughter, they plunge into the waves below, celebrating both life and memory.
