The members of S-Squad are looking for a break from their run of cold climate travails. So when a seemingly simple mission in Amazonia comes their way, they are looking forward to some welcome warmth. What they get is oppresive heat, biting insects, and a dredging operation on the river with a snake problem. A big snake problem. Soon they are in a fight for survival. The old snake gods of the river know the waterways much better than our Scottish squaddies. Are their wits, and bonds of comradeship enough to see them through?