Unraveling a Mystery and Social Media's Impact

Hannah Fry explores two tales of data and discovery.

Two couples are brought together by a tragedy and a tatty piece of paper, which reveals a serial murderer hiding in plain sight.

And, across the world in Singapore, a metro system is misbehaving wildly. The rail engineers and company officials are flummoxed. Can data save the day?

Produced by: Ilan Goodman and Lauren Armstrong Carter