If you suffer from paranoia it's best to steer clear of Dawn King's involving spy thriller Ciphers.
Everyone's out to get low-ranking MI6 operative Justine, or so it seems, after she swaps a career in marketing for the intelligence services.
When she dies in mysterious circumstances, her sister sets out to determine who's to blame.
There's no shortage of candidates queuing up. Was it the Russians, religious fundamentalists, her own bosses or a simple case of lover's revenge?
At one point in proceedings, a Russian doll changes hands during a murky encounter.
The curiosity perfectly sums up the drama. Both are intricately crafted and multi-layered, and in each case you're never quite sure when you've got to the bottom of things.
To add to the sense of duplicity and mistrust, the cast of four all double up, meaning there are plenty of unsettling moments where you're initially unsure who you're watching.
Grainne Keenan plays both Justine and her sister Kerry, the impressive Shereen Martin plays inscrutable MI6 chief Sunita and domineering art dealer Anouska, and so on...
Despite the odd occasion when the dialogue feels a bit jarring, director Blanche McIntyre keeps King's tightly-plotted script whirring along almost as busily as your brain cells trying to work out who did it.
Even after the curtain falls, there are lots of lingering questions to chew over, making it just the trick for Sherlock fans in need of a quick fix of sophisticated sleuthing.
* Ciphers is at the Bush Theatre, in Shepherd's Bush, until February 8.