Identify the main idea of this paragraph:

this ship is carrying kala fever serum to group one on woden. their own supply was destroyed by a tornado. group two—the crew your brother is in—is eight thousand miles away across the western sea and their helicopters can't cross it to group one. the fever is invariably fatal unless the serum can be had in time, and the six men in group one will die unless this ship reaches them on schedule. these little ships are always given barely enough fuel to reach their destination and if you stay aboard your added weight will cause it to use up all its fuel before it reaches the ground. it will crash, then, and you and i will die and so will the six men waiting for the fever serum