In Northern Ireland, from the late 70s to the early 90s, the IRA killed over 40 alleged informers.

But the man who often found, tortured and sometimes killed these people on behalf of the IRA

was himself an informer, a secret British army agent with the codename Stakeknife.

Who gets to play God? And why me? Why my family?

When lies are still being told to this day, who do you believe?

I wouldn't even know where to start, and I'm with the IRA.

Steakknife.

Listen first on BBC Sounds.

BBC Sounds, music, radio podcasts.

Hello, with me today, Radio 3 broadcaster Katie Derham,

presenter of among other programmes, in tune and The Sound of Dance.

She's also the face of the BBC proms, a strictly come dancing finalist,

and indeed last year's strictly Christmas champion.

With Katie is the author Matt Haig, whose non-fiction books include most recently Notes on a Nervous Planet. His latest

novel, How to Stop Time, is being developed as a film by Benedict Cumberbatch's company and his

latest book for children The Truthie, has just been published.

Katie, would you kick things off? What is your choice of a good read? Well, my choice, Harriet,

is Linda Grant's latest novel, The Dark Circle, which is a tremendous read, in my opinion, set in a

sanatorium for the sufferers of TB at a very key, interesting point in time for the history of that illness, 1949.

When a cure was on the horizon, the NHS had just come into being and suddenly into this very rule-ridden sanatorium in Kent, full of nice patients doing what they're told, come

NHS patients, particularly twins from the East End, Jewish twins, Lenny and Miriam, who are defiant

and don't want to believe that they're ill. They're only 19. They're full of spirit, and they shake

...