The Sewers Crisis

Aliens are coming. to get up your nose! They don't want our oil. They don't want our water. They don't want our Brussels sprouts. (Actually, neither do we.) They just want our snot! Jack and his friends have only one alien left to capture. The best is always saved for last, thought, so none of them should be surprised that this particular alien loves only one thing. poo! But once they've made a sickening descent into the sewers, the world should finally be safe.
Shouldn't it?