Out at sea, minutes and even seconds can make the difference between life and death. On the south coast of Devon, the crew of Salcombe lifeboat station are called to two of the highest level of emergencies at sea - a mayday call to a fisherman pulled to the bottom of the sea ensnared in his own fishing gear and a devastating fire on a boat 15 miles out in the Channel. Over 200 miles away in the waters off Anglesey, as they go to the rescue of a father and his 13-year-old son missing at sea, the crew of Moelfre station uncover a story of survival and heroism.

From first timers at sea to salty old skippers, the wrong conditions can catch anyone off their guard leaving them in need of rescuing. On the east coast of Ireland, the crew of Courtown's inshore lifeboat face one of their most challenging shouts ever - in deep water they must keep a teenage girl with suspected spinal injuries immobile and afloat for 40 minutes, knowing any movement could leave her paralysed for life. Meanwhile on the English Riviera in Devon, the Torbay crew have just minutes to find a capsized kayaker before she is dashed against the rocks, and in Dartmouth, an 81-year-old sailor, fallen overboard in the middle of the night, is left clinging to a rope for his life.

Keeping watch over the River Thames, the crew at Tower in central London, the busiest of the RNLI's 238 stations, are called to a man reported in the water eight miles downstream. On arrival, they discover a river bus already on the scene and their crew desperately trying to hang on to the unmoving man before he disappears under the water. At one of the most remote stations, Trearddur Bay on Anglesey, the crew are called to an inaccessible coastal fishing spot, where an angler has plunged face first down a cliff onto rocks. With no helicopter available, the crew and their small inshore lifeboat are the only option to get him to urgent medical treatment. While in Portsmouth, gale force winds and a churning sea make a routine rescue particularly challenging.

In Brighton the crew are called out to what they think is just a routine job - towing a yacht that has lost power back to harbour - but a sudden spring squall and mountainous waves leave the crew fighting to save the yacht and themselves from being dashed on the shore. Off the east coast of Ireland, the crew of the small fishing village of Howth respond to an emergency call from a family on a local beach - a teenage girl out on a sailing dinghy has capsized and is now being swept out into the Irish Sea. While on the island of Anglesey, the crew of Moelfre are also heading out to help a family in trouble - two women have swum out to save a friend's young son being blown out to sea on an inflatable, but it quickly becomes the rescuers that need saving themselves

In Torbay in Devon the seas are often crowded with sailing craft of all shapes and sizes – when two collide the Torbay lifeboat crew are called out to provide emergency medical assistance for a potentially life-changing injury. On the south coast of Wales, the Porthcawl crew have just seconds to spare when two teenagers on holiday get caught on a rocky outcrop by a large swell and a rising spring tide. While in Yorkshire, the Flamborough crew have to pluck a man from danger after he jumps off a hundred-foot cliff for a dare.

There are many reasons why the thousands of yellow-wellied volunteers first joined up, but they all share a common desire to help those in trouble. At Anstruther station in Scotland, one of their newest helms, George, takes charge for his first shout to a serious medical evacuation. A woman has slipped on one of the most notorious parts of the station's patch, the Chain Walk, where walkers have to negotiate steep cliffs while hanging on to chains hammered into the rock. On the north coast of Devon, the crew at Appledore station make a life-or-death dash to rescue two teenagers caught in a cave being flooded by the tide and pounded by waves, but arriving at the scene they discover that saving the young couple will mean putting themselves in danger. And when Storm Henry hits the British Isles and has shipping running for safe harbours, a cargo ship loses all power and is left at the mercy of the waves and 90-mile-an-hour winds. As she drifts inexorably towards the rugged cliffs of north Devon, two lifeboats are launched but even with their combined power they face a losing battle trying to tow the huge ship out of harm's way

On the north coast of Kent, new crew member Ruth is on board for one of her first ever shouts. Off the Essex coast, the crew of West Mersea station launch to reports of a life raft in the North Sea. 10 miles along the coast at Clacton the crew get a call in the middle of the night to look for two people in the sea.

For the thousands of volunteers who guard our seas and waterways, saving other people can mean making sacrifices in their own lives. Volunteer and doctor Adam makes a 500-mile round trip every time he puts in a shift at Tower Lifeboat Station in the heart of London, but his medical skills prove invaluable when the crew are called to help the police try and save a man who is stuck under a pier on the Thames with the tide rising. In north Wales, when police officer Vinny isn't patrolling the streets of Rhyl, he volunteers for the lifeboat crew. When the pagers go off one summer evening, Vinny finds himself heading out into the darkness to try and rescue two teenage boys who have chased a wayward football into the sea and get caught in a treacherous current. While across the Irish Sea in Dunmore East, the lifeboat crew's evening is interrupted by an urgent call to a motor boat stranded several miles out and taking on water.

As storm Ophelia hits the British Isles, on the south east coast of Ireland the pagers of the Rosslare crew go off - a small yacht with three people on board is caught in one of the worst storms in living memory. In Devon, the crew at Appledore race an incoming tide to try and reach a man stuck fast in quicksand, while on the north coast of Cornwall the crew of St Agnes must battle through huge breaking waves to reach two young boys being swept out to sea in a deadly rip current.

Off the packed beach at Blackpool, the crew race after a teenage girl being swept out to sea on an inflatable dinghy. While on the miles of long sandy beaches at Rhyl in north Wales, amongst the holidaying crowds two girls get caught in a deadly current while swimming just a few metres from shore. And on the Cornish coast a woman, trying out the extreme sport of coasteering for the very first time, falls several metres down a cliff face onto a beach with a fast incoming tide.