The RNLI respond to over 9,000 shouts each year — and what often gets people into trouble in the first place are the hidden dangers. In Porthcawl, on the south-west coast of Wales, the crew receive a call about a swimmer who's been swept out to sea in a rip current — as his wife and son watch on helplessly from the beach. On the Cornish coast, the Sennen Cove and Penlee crews respond to reports of a 31,000-ton cargo ship that's about to run aground on the Wolf Rock lighthouse, ten miles from Land's End. On the east coast of Scotland, the strong offshore winds at North Berwick cause the crew to be called out to two shouts in quick succession. And on the Thames, the Chiswick crew race to the rescue of a party boat that has lost engine power — and is now drifting dangerously upriver.