Kate is a young woman who has a habit of making bad decisions, and her last date with disaster occurs after she accepts work as Santa's elf for a department store. However, after she meets Tom there, her life takes a new turn.
| Kate Andrich | Emilia Clarke |
| Tom Webster | Henry Golding |
| Santa | Michelle Yeoh |
| Petra Andrich | Emma Thompson |
| Marta Andrich | Lydia Leonard |
| Ivan Andrich | Boris Isaković |
| Dr. Addis | Rebecca Root |
| Police Woman Crowley | Ingrid Oliver |
| Police Woman Churchill | Laura Evelyn |
| Joyce | Patti LuPone |
| Nathan | Calvin Demba |
| Jenna | Ritu Arya |
| Rufus | Ansu Kabia |
| Alba | Jade Anouka |
| Theatre Director | Rob Delaney |
| Theatre Producer | Peter Serafinowicz |
| Casting Director | Sara Powell |
| The Dane (aka ‘Boy’) | Peter Mygind |
| Andy | Amit Shah |
| Ed | Maxim Baldry |
| Sarah | Margaret Clunie |
| Ice Show Director | Sue Perkins |
| Klaus the German Clown | John-Luke Roberts |
| Young Kate | Madison Ingoldsby |
| Young Marta | Lucy Miller |
| Oscar | Bilal Zafar |
| Danny | Ben Owen-Jones |
| Arthur | David Hargreaves |
| Tom | Joe Blakemore |
| Dora | Anna Calder-Marshall |
| Traffic Cone Man | Leon Delroy Williams |
| Croatian Woman | Jassie Mortimer |
| Croatian Man | Michael Matovski |
| Angry Man on Bus | Jake Lampert |
| Moroccan Vendor | Liran Nathan |
| Moroccan Vendor's Wife | Laila Alj |
| Guy in Pub | David Mumeni |
| Man in Audience at Homeless Shelter Benefit (uncredited) | Andrew Ridgeley |
| Homeless Person (uncredited) | Jacqueline Ramnarine |
| Nurse Jane (uncredited) | Nichola Jean Mazur |
| Fabien | Fabien Frankel |
| Geoff Mafia Boss (uncredited) | Rene Costa |
