It's the story of a ship's captain who falls apart under pressure. His mental state is demonstrated in several ways, notably by what's referred to as the "strawberries incident", when Queeg pushes through a relentlessly obsessional and absurd quest for whoever stole the wardroom's strawberries, and how it was done.
In a moment of crisis, when Queeg makes a faulty decision in a heavy storm, he is relieved of his command by two senior officers, put up to it largely by Lieutenant Keefer, an amateur psychologist and sure that Queeg is paranoid. Back on shore, the two who relieved the captain (but not the more junior Keefer) are court martialled. However, under pressure in court, Queeg crumbles to a pathetic wreck.
The book has many messages, but the main one is that here is a senior leader, with a proud record, brought down by what we would now call stress, an inadequate word to describe the pressure on a ship's captain in the Pacific War. At the very moment that he needs help, indeed, all but pleads for it to the extent that his position permits, those around him choose instead to make gossiping fun of him and, ultimately, to destroy him.
Wouk's story is as clear, and moral as a parable. It's about humanity and compassion, and the fact that they are qualities which can and should outweigh considerations of hierarchy and authority. So before you gather in groups to whisper about your leader, or make up unkind nicknames, or plot to complain to head office, or start making a diary of events, think instead about whether, and how, you can offer support and an understanding ear. There are so many things you can do. You can say, "Don't forget we're still here?" Or you can go in, shut the door, and say, "I've brought you coffee, do you want to chat about things?"
All too often, alas, as on the "Caine", some less worthy instinct leads us instead to latch on to weakness, which, of course, is a fault of human nature that we constantly preach to our children about.