The BBC4 website seems to be timing-out - no doubt as fans of Spiral click on it. I'll update this post when I can get through!
By my reckoning, this makes Waking the Dead, Marple, Harper's Island and Spiral all on one night...
Update: Spiral will be on BBC4 at 10pm, for 50 mins:
When a charred corpse is found in the boot of a car in the suburbs, Berthaud's police team are called to the scene along with the prosecutors Roban and Clement. So begins an investigation which forces the team into the broken, gang-ruled suburbs of Paris, and once more to the door of shady lawyer Josephine Karlsson.