Beginning at the fabulous coral reef of Ningaloo in Western Australia, intrepid marine biologist Mark Meakin attempts to unravel the mysterious wanderings of the biggest fish in the sea.

Whale sharks grow to over 12 metres long but are gentle, filter-feeding giants; even Mark's five-year-old son can swim alongside them. Yet no-one knows where they go once they leave Ningaloo's turquoise lagoons.

Using satellite tags and photo IDs, Mark tracks them to the white coral beaches of the Seychelles and the tropical jewel of Christmas Island, where bright-red land crabs begin their annual migration. It's hard work, taking in 20 failed satellite tags and countless frustrating dives, before Mark makes a breakthrough which doesn't just add to our understanding of these huge 'dinosaur fish' but offers crucial information about how the whale sharks of Ningaloo can be protected better.