The Big Show: Mrs Wilson, Tues, 9pm, BBC1

In the intriguing new BBC drama Mrs Wilson, actress Ruth Wilson plays her own grandmother Alison – who learns her spy husband had three wives.

Mixing romance, bigamy and the murky world of MI6, this true tale is stranger than any fiction.

‘I would tell people the story, and they all said to me, you’ve got to get this made,’ says Ruth, who is best known for The Affair and Luther.

Luther star Ruth Wilson says TV role made her "hate" her serial bigamist grandfather

The series begins when her grandfather Alexander (Game of Thrones’ Iain Glen) suddenly collapses and dies.

As Alison grieves, she opens the door to a woman who introduces herself as Gladys – and tells her she was Alexander’s wife.

The story unfolds with flashbacks to Alison and Alexander’s first meeting and their courtship. Then it returns to the present when she begins to search for answers about her late husband.

She quizzes the secret service agent’s MI6 handler (Fiona Shaw) about his undercover work in the Second World War.

And she’s gobsmacked to find out that Alexander had a third wife, Dorothy (The Durrells and Bodyguard star Keeley Hawes). Dorothy married Alexander while he was stationed in Lahore in the 1930s.

In real life, Alison wrote a memoir, which screenwriter Anna Symon used as her starting point for scripting Mrs Wilson. Anna then spent hours talking to relatives, teasing out their personal memories, and sending drafts back and forth to get the events as accurate as possible.

Ruth admits filming the three-parter was an intense experience. ‘It’s probably the hardest thing I’ve done,’ she says. ‘There were so many pressures. The pressure of the family. The pressure of whether you’re performing in the right way.’

But putting the story together had a happy outcome for her wider family, who this summer came together for the first time.

‘It has been amazing,’ says Ruth. ‘It has completed my story a bit. I realised where my proclivity for acting and storytelling came from – the greatest actor of us all, my grandfather!’

* Mrs Wilson, Tues, 9pm, BBC1