In the first episode, a father and daughter find themselves treading water for almost an hour, hundreds of metres out at sea, after being swept out by a rip current. In Kinsale, Ireland, three fishermen swim for their lives as their trawler is smashed on to rocks. And in London, an unlucky tourist is minutes from hypothermia after his attempt to take a selfie lands him in the Thames.

Off the coast of Bridlington, a kayaker has been missing for an hour, and only the crews' expert coastal knowledge can help track him down. A crew member on his first shout races to a dinghy capsize to find a man losing consciousness in the water. And when a fishing trawler sinks off the coast of the Shetland Islands, the fishermen and RNLI crew aboard must swim for their lives.

In Ireland, the Castletownbere crew race to rescue a lone yachtsman who has lost his mast and is drifting powerless in 10-metre waves, 45 miles out to sea. In Minehead a woman on a clifftop walk has gone missing, and after 17 hours the crew are called to search the shoreline. And for an injured horse rider on a remote beach, the Porthcawl crew are the only way to emergency medical help.

In Bangor, Northern Ireland, crews are tasked to find two teenage paddle boarders, blown offshore towards nearby shipping lanes. The Tenby crew in West Wales must race to a dog who's fallen over a cliff - before worried members of the public attempt to rescue it themselves. And on the North Norfolk coast, the harrowing hovercraft rescue of three young sisters still brings back painful memories for the Hunstanton crew.

Every day around the UK, an army of unpaid volunteers put their lives on the line to try and save complete strangers. Saving Lives at Sea tells the story of the ordinary men and women of the Royal National Lifeboat Institution (RNLI) who, across the country, are ready to launch their boats and race to the rescue within minutes of a cry for help - 24 hours a day, 365 days a year, whatever the weather. Using footage shot on crews' own cameras, this series takes us right into the heart of the action, capturing the unpredictable work of the RNLI in never-before-seen detail. In south west Wales, the Tenby crew race to a kayaker with suspected back and neck injuries after being caught out by a freak wave. Neighbouring Cornish crews must join forces in an epic 11-hour battle to stop a 3,600-tonne coaster breaking up on the rocks. And the Dart and Salcombe crews are astonished to be paged to the biggest shout of their lives.

In episode six of this 12-part series, on one of the hottest days of the year, the Dover crew race to a Channel Swimmer who's collapsed within sight of the French coast. In Mudeford, there are growing fears for a dinghy sailor who is four miles out in rough seas and refusing to accept help, and the Tenby crew are called to a runaway yacht just metres from running aground.

When a climber falls in a remote cave on the Gower Peninsula, the Mumbles crew are called in to search and rescue. In Portreath, lifeguards battle to save a teenager who is determined to surf despite red flag warnings. And on the Isle of Wight, the Yarmouth crew must locate a man in the water amongst over a thousand boats competing in the Round the Island Race.

In Ilfracombe, a father and son find themselves in danger after jumping in to rescue a drowning dog. The Minehead crew must scour the cliffs and shoreline after a young woman goes missing in a distressed state. And when they're paged to a man seen entering the Thames, the Tower crew face the possibility they may not find him in time.

The Aberystwyth crew must improvise when a local paraglider crash-lands at the bottom of steep cliffs. When an adventurous seal is discovered on the steps of a block of flats, Redcar's newest recruit is first on the scene. And in Minehead, a challenging rescue forces an inexperienced crew member to consider her future.

As the summer sun comes out, so do the fun seekers, and crews around the country get ready for action. In Southend, a family of five out sightseeing are a mile off shore and waist-deep in water after being caught out by the tide. The Shoreham crew are paged in the early hours after a drunken festival-goer jumps in the river. And the Brighton crew fear the worst when a man tombstones off the pier at low tide.

When an early morning dog walker spots a flare off shore, the Rhyl crew race to one of the most mysterious shouts they have seen. The Lowestoft crew find themselves paged to help to a sailor who doesn't want to be rescued. And at Tower, a good samaritan is clinging on for his life after trying to rescue a dog which has jumped into the Thames.

In Tenby, police searching for a boat thief call for lifeboat assistance. The Mumbles lifeguards and lifeboat crew race to help two kayakers adrift in a boat laden with beer. And when two yachts capsize off Portsmouth, the crew must make fast decisions about who to rescue first.