When Robin Griffiths embarks upon the restoration of a stained-glass window in a thirteenth-century church, little does she comprehend the stakes involved. The more slivers of glass she pieces together, the more she realizes things are not what they appear to be in the seemingly cozy hamlet of Bilbury. Piece by piece, sliver by sliver, the window is revealed in all its glory. But will she survive with her sanity intact, or will reawakening the image in the window prove to be her undoing?

The premise of ‘Mosaic‘ screams gothic horror – an introverted, socially isolated woman becoming increasingly disturbed by the apparently demonic image that she’s bringing back to life as she restores a stained-glass window in a remote, long abandoned thirteenth-century church so I was expecting a story that was heavy foreboding and Hammer Horror vibes. Catherine McCarthy’s storytelling was subtler and much scarier than that.

Robin Griffiths, the artisan from whose point of view ‘Mosaic’ is told, comes across as a very down-to-earth person. The day-to-day details of her life are reassuringly normal. Yes, Robin has some mental scarring from being raised to be the scapegoat in a narcissistic family but she is a survivor: practical, independent and building a new life for herself. We see Robin assessing her new client, planning the execution of the project and interacting with the builders who are repairing the roof of the church she’s working in and everything seems normal. Well, almost everything. There are small discrepancie and unexpected microaggressions that raise red flags here and there but they’re hard to hold on to when everything else is so normal.

I was fascinated by the way in which normality slowly recedes, like an outgoing tide, leaving Robin mired in something strange and deeply disturbing. Catherine McCarthy controlled the story’s pace perfectly to provide a continuous ramping up of tension. It starts with small oddities: the graveyard having become a wilderness with yew trees growing down into graves, pinning the skeletons in place, and gravestones so eroded that the names of the dead are unknowable. Then there is the strange behaviour of some of the locals, the creepiess of the client, the odd flashes of something hidden or possibly imagined in the old man tending the graveyard, all of which unsettle Robin but don’t frighten her.

Then there is the pull of the image of the stained-glass window which Robin is having to piece together like a mosaic from fragments of old glass, like doing a jigsaw puzzle without an image to guide her. It fills her imagination, as you’d expect it to. Except, the image that’s emerging in her mind is… wrong. Robin knows this but still loses herself in it, drawn to the sensual power of its imagery, texture and colour.

As Robin tries to manage her growing unease, it becomes clear that she’s carrying more mental scars than were originally apparent, making her a less reliable narrator and making me wonder how much of what Robin was seeing was only in her head.

The first half of the book is tense and disturbing without falling over the edge into the incredible. Then. as Robin, now working alone in the church, becomes lost in questions about the history of the church and the window, she heralds the shift into darker territory by telling herself:

 “The answers I seek might well lie beneath my feet, in the crypt.”

Nothing good ever comes from going down into an unlit crypt in which a previously bricked-up alcove with strange marking on its walls has just been discovered.

The last third of the book builds into full-blown gothic horror with a spectacular denouement.

I wasn’t quite sure what to make of the ending. I’m an atheist and habitually sceptical so I struggled with the supernatural parts of the story. Then I realised that the ending can be read in two ways: one in which everything happens as described and one in which most of it happens only in Robin’s head. Either reading is deeply disturbing.