Season 4 is a two-part Christmas special set two years after Kate's tragic death, which sees Caroline (Sarah Lancashire) coming to terms with yet more changes in her life.
To Celia's (Anne Reid) dismay, Caroline takes on a challenging new headship role at a troubled state school and buys a rundown farmhouse nearby. Is there more to this big upheaval than she's letting on - and will her move prompt her mother and Alan (Derek Jacobi) to finally find a place of their own?
Meanwhile, Gillian (Nicola Walker) is struggling to come to terms with the unusual activity that keeps happening in the barn. With issues from her past coming back to haunt her, will she let them affect her relationship with Robbie (Dean Andrews)?
With Celia trying to rope a reluctant Alan into her new amateur dramatics hobby, Caroline negotiating a tricky new relationship and Gillian fighting a compulsion to confess to Robbie how his brother really died, life for these characters is as complicated as ever.
Last Tango in Halifax Christmas special is a 2x60 minute season made by RED Production Company for BBC One. It is created and written by Sally Wainwright, produced by Karen Lewis and directed by Juliet May. Executive Producers are Nicola Shindler and Sally Wainwright for RED Production Company and Matthew Read for BBC One.