Tonight is the fifth episode of series two and viewers can see Celia reluctantly introducing Alan to her sister, Muriel.
Caroline is stunned to learn that Kate is pregnant and receives a further blow from John.
A drunk Gillian shares a dark, sinister secret with Caroline.
The drama is on BBC 1 tonight(Tue) at 9 pm.
Writer Sally Wainwright, who was brought up in Calderdale, is currently working in the area where her latest work Happy Valley is being filmed and that will also be screened on BBC 1 next year.
The thriller follows a police sergeant named Catherine (played by Sarah Lancashire).