Once upon a time, in an attic full of half-finished gadgets, there lived an engineer called Toly. He’d spent years getting computers to talk to each other, and he’d noticed something about them. Like cousins at a wedding, they almost never agree on what time it is.

One night the smallest clock on the wall started ticking louder than the others. Then it hopped off its nail, landed on the desk and ticked right at him. Tick. And again. Tick. It wasn’t asking permission. It just had no intention of stopping.

Toly picked up his pencil. “Fine,” he told the clock. “Say you never stop. What could a whole network do with that?”

This was the problem Toly kept coming back to. A blockchain runs on lots of computers spread around the world. Each one keeps its own copy of the ledger, and they all have to agree on what happened and in what order. There’s no central clock they all trust.

Every computer has its own clock, of course. But clocks drift, messages turn up late, and some of the computers might be broken or lying. Asking a network “what time is it?” is a bit like asking a crowded room to shout out the time all at once.

So Toly drew arrows. Box, arrow, box, arrow. Each box would hold a fingerprint of the box before it. Tick watched closely, then tapped the last box with one tiny foot, as if to say and keep going.

Toly tried an experiment. He asked every clock in the attic what time it was. The cuckoo clock said a quarter past two. The grandfather clock said twenty to three. The kitchen timer said “BEEP”, which didn’t help.

None of them was exactly wrong. They’d started at different moments and drifted at different speeds. Now imagine thousands of computers on different continents, with messages taking different routes between them. That’s a very loud attic.

Tick just kept counting. It had no idea what time it was in Lisbon. All it knew was that this tick came after the last one, and Toly started to think that might be enough. First, though, he wanted to see the problem out in the world, in a town where nobody could agree on anything. Least of all Tuesday.