Deep beneath the floor of the Atlantic Ocean, scientists and engineers attempt the most daring and audacious scientific project of all time: the construction of an undersea tunnel between Great Britain and Canada; linking Land's End with Labrador. Canadian and British teams work simultaneously at either end, to converge in the middle. Using scientific methods to fight the crushing pressure and geological and marine perils involved, the brave workers face a far greater hazard - the danger within - from saboteurs!