Colin Burstead (Neil Maskell) has hired a heritage mansion for a New Year's Eve party for his extended family and various hangers-on, with his wife Val (Sura Dohnke), teenage daughter Fran (Nicole Netlleingham) and infant son Jamie in tow. Colin's mother Sandy (Doon Mackichan) – the family's matriarch – dramatically injures her ankle before she has even crossed the manor house's threshold. Her indebted husband Gordon (Bill Paterson) is desperately trying to secure a life-saving loan that Colin simply will not grant him. Uncle Bertie (Charles Dance) is secretly ill, and knows this might be his last time seeing the clan all together. Meanwhile, self-deceiving Sham (Asim Chaudhry), the son of Sandy's best friends Maya (Sudha Bhuchar) and Nikhil (Vincent Ebrahim), has gatecrashed the party in the hope of winning back his ex-girlfriend Lainey (Sinead Matthews), who is doing the catering.

All these little tensions and dramas are overshadowed by the return of Colin's black sheep brother David (Sam Riley) to the family fold after an absence of five years, along with his German girlfriend Hannah (Alexandra Maria Lara). Invited by Colin's sister Gini (Hayley Squires) against the advice of her husband Warren (Mark Monero), as a surprise for Sandy, David immediately finds himself less than welcome, and not just to his ex-wife Paula (Sarah Baxendale) – but over the course of the evening, his presence will shift the family's power dynamics.