‘He made test impellers using 3D printers, but tooling up to put the kit in production would have cost over a hundred grand. He didn’t have the money and he was scared to show the big Chinese drone manufacturers, because they’re notorious for ripping off ideas.’

‘You all need to see this,’ Gerard said, holding out his phone.

Gerard had cued up a YouTube video, titled Fuel Air (Thermobaric) Explosion. The clip lasted twenty seconds, showing a fireball erupting out of a metal cylinder no bigger than a fire extinguisher. The mid-air explosion incinerated three large trees and made a shockwave that caved a metal roof like a boot on a soft-drink can.

‘That’s a fuel air weapon,’ Gerard explained. ‘Nozzles disperse a fine mist of aviation fuel into the air. The tricky part is that the mixture depends on atmospheric conditions, but if you get it right you make a huge fireball with a tiny amount of liquid. John Pack’s impeller can be configured to make explosions like this.’

Kamila looked at Georgia accusingly. ‘Your dad developed that?’

Gerard gave one of his superior snorts. ‘John can’t have realised his impeller could be weaponised. If he had, he’d have had defence companies queuing up to fund his research.’

Zac looked aghast. ‘You’re seriously talking about using one of John Pack’s survey drones to create a giant fireball and blow up … whatever …?’

‘The government!’ Gerard suggested cheerily. ‘Well, some of it … The Russians add lightweight plastic flechettes to their thermobaric weapons. They can mince a person two hundred metres away …’

Georgia was horrified, but intrigued.

‘Survey drones aren’t as zippy as the racing drones I used to fly,’ she thought aloud. ‘But they’ll do sixty kilometres per hour if you set the trim properly. If you flew to a target at top speed, you could probably blast fuel out of the nozzle before anyone shot the drone out of the sky …’

Elodie raised her arms in the air and sounded alarmed. ‘What are we talking about here?’

‘The radical in RAGS,’ Gerard said determinedly.

Zac found the whole thing so mad he laughed. ‘Gerard, I have zero desire to spend my next twenty years in prison.’

Georgia felt embarrassed by her flash of ill-considered enthusiasm. But Gerard kept rambling.

‘It doesn’t have to be fuel,’ Gerard explained. ‘There are guys at my lab in King’s College working on attenuated viruses for pest control. My old lab partner wants to build a synthetic virus that stops the Killer T cells that control rodent immune systems. If they made a human version, we could load it in a drone. Wipe out a state banquet, or the entire platform at a party conference.’

Kamila put a hand on Gerard’s back. ‘Darling, you’re getting carried away. Radical, yes. Mass murder, no.’