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Today, I want to take you to Singapore, a thriving city on an island, bustling with skyscrapers, a high-tech business hub connecting Southeast Asia with the West.

It was here in 2016 that a driverless metro system started glitching wildly.

Trains crammed with commuters began stopping, suddenly, often deep inside tunnels.

And no one could figure out why.

I'm Hannah Fry, a mathematician who studies patterns in human behaviour.

And from BBC Radio 4, this is uncharted, tales of data and discovery.

This is a series about how numbers and graphs can help you to map the invisible,

about how plots can be rich with hidden depths and unheard stories,

and about how sometimes, if you know where to look,

there is mystery and drama and intrigue to be found, all concealed within a few simple lines on a page.

Singapore is a tropical city state known for being extraordinarily clean and smartly turned out.

The parks are carefully manicured. The roads are smooth and well maintained and its

pavements are litter-free. Famously, chewing gum is banned. And it is also home to a very

badly behaved train line. On the face of it, the Singapore metro system is as fancy as the city.

Mostly built since the 1990s.

It is modern and air-conditioned and largely driverless.

The trains are in charge, coordinating their own passage, bouncing signals off each other and the stations they

pass through. The whole network smoothly automated.

Passer of Punjab, please mind the platform yet.

Until, that is, the summer of 2016, when without warning, one line went rogue and through this well-regulated city into uncharacteristic disarray.

So I first heard about the problems at the end of July of 2016.

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