Just exactly what can you see from the top of the London Eye?

That's the question Millie Ravensworth (actually two writers: Heide Goody and Iain Grant) and I asked ourselves when we started planning Death on the Thames.

In the book, Diana Bakewell is riding the Eye with a group of customers of Chartwell and Crouch Tours, when she witnesses something suspicious down on the ground.

The customers this time aren't just any old punters. They’re a group of extremely wealthy businessmen including Kamran Dadashov, the father of Alexsei. Alexsei is Diana's neighbour in the flat below hers in Pimlico, and he’s also dating Zaf, her fellow tour guide. Which throws up tensions, as Kamran has no idea his son has a boyfriend and is angling for him to marry a nice Russian girl.

Alexsei has no intention of marrying a Russian girl chosen by his father, just as Diana has no intention of keeping quiet when she reaches the ground and reports what she saw to the police, only to be told that she's mistaken.

Diana may be in her sixties but, as she'll firmly inform anyone who suggests otherwise, she's fully in control of all her mental faculties. No doddering old women here, thank you very much.

Diana is convinced that she really did witness something suspicious, from way up inside a pod on the London Eye. And so she decides to take matters into her own hands and rope Zaf in to help her investigate.

It's not long before she realises that not only did she witness a crime, but that the members of the tour group with her at the time may be involved...

Researching Death on the Thames was huge fun. We knew we wanted to get to know the locations better, and most importantly, work out a murder mystery that could take place in or around the London Eye.

In the summer of 2023, we booked ourselves tickets on the Eye, with a view to plotting our murder.

At that point, we hadn't yet worked out exactly how the murder would take place. We imagined it as a potential locked room mystery, inside one of the pods as it circled its route. But we'd already done a locked room (well, bus) mystery in Death at Tower Bridge. So then we tried to work out how someone might enter or leave one of the pods while it was moving. Could you throw someone out, or conduct a chase across the struts of the massive wheel that supports the pods?

We examined the emergency exit and the main doors to the pod, while trying not to look too suspicious (occupational hazard for a crime writer). And it became clear that getting in and out of a pod was impossible.

So we went back to square one. Peering out of our moving pod, we tried to identify locations outside the Eye itself where the crime would take place.

On one of the wheel's supports, perhaps, or the access stairs leading up them? Maybe on the pontoon that floats in the river beneath the Eye?

[Photo: view downwards from a London Eye pod]

Eventually we came up with the idea of incorporating the River Thames itself. It later turned out to be a wise decision, when we discovered that we wouldn't be permitted to call the book Death on the London Eye, as originally planned. It turned out that ‘London Eye’ is trademarked, and so we switched to Death on the Thames.

A better title all round, I think.

So by the time we reached the ground, we had a plan for our murder mystery. One we were able to elaborate on by then walking around the area around the Eye and working out the lines of sight.

(Why none of us has been arrested on suspicion of terrorist activity, I'll never know.)

And that's how we devised the murder at the heart of Death on the Thames. But to find out how Diana and Zaf solve it, you'll have to read the book...