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.

All human relationships are here on Open Book this week,

from fleeting teenage lust to lifelong companionship.

But first...

Every breath you break, every step you take, I'll be watching.

Every breath you take by the police, seen by some as the ultimate love song,

but described by Sting himself as a very, very sinister song about jealousy and obsession.

That blurred line between ardent love and destructive stalking has been explored in novels

from the talented Mr Ripley to to Enduring Love and Lolita,

and most recently, the huge Netflix hit, You, based on the novel by Caroline Kempneys.

Now, two books published this month continue the theme.

Dream Sequence by Adam Folds charts a chapter in the life of handsome British actor Henry Banks,

star of a Downton-like series called The Grange,

and his obsessive fan, Kristen, who's convinced they're meant to be together.

...