Citizens living in Fortitude, an Arctic town hailed as the safest place on Earth, are rocked to the core by the murder of one of their own. A detective is quickly flown in from out-of-town to assist the local Chief of Police with the investigation of the town's first-ever violent crime and the two men must work together despite the deep mistrust each has for the other.

It's 1963, and Alison Wilson returns home to husband Alexander -- shortly before his sudden collapse and death. Blinded by grief and focusing on her two teenage sons, Alison is bewildered when a woman arrives at the door claiming to be Alec's 'real wife.' Alison sets out to discover who Alec really was; dissecting their 1940s romance, and her husband's mysterious career in the secret service.

Alison is on the tail of the elusive 'Dorothy,' finding photographs of her from Alec's time in India. After speaking to Alec's handler and hearing that their 'relationship' was likely a cover story, Alison traces Dorothy to Yorkshire and insists on the truth. Back in the 1940s, Alison struggles with the aftermath of Alec's decisions, forced to raise her young family in poverty in wartime London.

It is Cathy's first Valentine's Day since she lost her husband. Her brother Derek comes round to keep her company but his partner Pauline wishes that she was anywhere else. Cathy's son Jason has some surprising news for her and when Michael turns up unannounced he's concerned to find that Cathy has received a Valentine's card.

It is a hot summer's day, and while Kelly and her cousin sunbathe in the garden, Cathy is getting ready to go for lunch with a new, male friend. Michael is taking her and is keen to find out more about this friend.

Lynley and Havers question Tessa, who paints a disturbing picture of life with William. To fill in the missing pieces, Lynley and Havers begin to search for Roberta's sister, Gillian. Strangely, opinions about her vary dramatically from one person to the next.

Cathy's family visit to help her clear out her garage, her brother and his partner turning up fresh from a game of golf where they've made friends with a millionaire. Kelly's mum comes round to take an old fridge and Cathy sees a new side to her. Michael helps out too and faces a decision.

This is the story of the first celebrity couple: Elizabeth Taylor and Richard Burton were the original fabulous stars, and many were enthralled by their illicit romance, two tempestuous marriages, frequent break-ups and extravagant reunions.