Salisbury becomes the scene of a major international incident.

Sergei Skripal and his daughter Yulia are found poisoned on a park bench.

Then, an astonishing discovery: he’s a former Russian spy and they've been poisoned with Novichok, one of the deadliest substances in the world.

Parts of Salisbury are locked down as police try to find the poison.

This episode has been updated to reflect Sergei Skripal’s role as former GRU officer.

This episode was made by Marie Lennon, Andy Howard, Tom Ryan & Dan O’Brien.

Executive production by Mary Sanders and Naomi Wordley.