Vigil BBC1, 9pm

As we left things last week at the cliffhanger of the penultimate episode of the submarine thriller, detective

Amy Silva (Suranne Jones, right) was struggling to keep her head above the surface. Some of us might well have been nodding in recognition of that sense of battling to stop drowning – though in the case of viewers, not from water but the complexities of an increasingly bewildering plot.

Yes, sometimes we have been left scratching our heads trying to keep up and experts have cavilled at the credulity-stretching sequence of events on board the usually disciplined Royal Navy vessel, but this has been an engrossing, rip-roaring tale.

In a thrilling conclusion, we find out how far the network of traitors spread and the reason for the death of seaman Craig Burke that sparked the investigation. ★★★★★