When the Empire State Building comes crashing down, both Ned Cook and his cameraman, Joe, they fall into a deep cavern. The men are trapped with water seeping into their hollow from an uncharted underground river.
This is clearly a job for Thunderbird 4, which could navigate up the river from its outlet in the bay, but first Brains has to find the way into the river, and plan the operation.
On Tracy Island
Brains studies the map of the underground rivers
