In the first episode, a retired nursery teacher gets herself into danger when attempting to rescue her two dogs after they became cut off by the rising tide. In Wales, one volunteer crew member is washed off a cliff into the sea trying to rescue a concussed spearfisherman, and, in Blackpool, a rescue in a force seven gale goes badly wrong, putting all three crew members' lives in jeopardy. When torrential floods hit Cumbria shortly before Christmas the volunteers are again on hand to try and rescue families trapped by the rising waters.

The volunteers of the Royal National Lifeboat Institution staff more than 230 stations covering even the most far-flung areas of Britain's coastline, but the busiest station by far is actually miles from the sea, on the River Thames in central London. It was established after the Marchioness pleasure cruiser sank in 1989, claiming the lives of more than 50 people. While it might look benign, the Thames is actually one of the most dangerous stretches of water in the UK. The volunteers are called from their beds in the middle of the night to try to rescue two students who have jumped naked into the river while high on LSD. At the coast in Newquay, the volunteers and coastguard helicopter are scrambled to try and help a 12-year-old boy on a Cub Scout trip who has fallen badly and has suspected spinal damage. Eastbourne lifeboat station covers a stretch of coastline which includes Beachy Head, so they have had to become more familiar with death than most. Recovering the body of someone who has taken their own life is a duty the volunteers see as an important service to the family who have lost a loved one.

In Cornwall, newest recruit, 18-year-old Shaunna, is following in her grandfather's footsteps. After a successful first rescue of a teenage holidaymaker, she has hopes to one day become Newquay's first helmswoman. In the remote fishing village of Oban on the west coast of Scotland, the RNLI have another new 18-year-old recruit. Young Andrew and the rest of the crew are given a painful reminder of the dangers all lifeboat volunteers face when they are woken by their pagers in the middle of the night to try and rescue the captain and crew of a fishing boat that is sinking having run aground in the middle of a storm. Volunteering with the RNLI inevitably means encountering and risking death, and it is a sacrifice that takes its toll on the crew-members and their families. But, coming as it does with the opportunity for ordinary men and women to save human life, it also has its own very unique rewards.

In the summer months, millions of Britains flock to the UK's 11,000 miles of coastline. As more and more of us have lost our connection with, and understanding of, the seas that surround us, it's all too easy to be caught out by the water - making it the busiest time of year by far for the RNLI. The army of unpaid volunteers has to contend with everything from overly ambitious novice sailors caught in a storm, to a little girl who has become trapped in the rocks below the high-water mark. The dangers of the water are further put into perspective when a father gets himself into serious difficulties after swimming out to try and rescue his young son, whilst a YouTube prankster deliberately flings himself from Tower Bridge for 'a dare'.