Like any student of history, Sam Sheridan has long expected, as he says, that “the s--- is going to hit the fan some day.” Having a child didn’t do much to lessen his obsession with Armageddon.

Some men might talk things through with the wife or a friend or a counselor. Others might simply ignore the obsession and get on with the changing of diapers and the warming of bottles. But Sheridan takes a third road. As he relates in his enjoyable new book, The Disaster Diaries, he decides to train for the unthinkable: the life of a postapocalyptic survivor. He pursues the skills that he will need to defend his family in an imagined world without rules.

We are not talking about planning for ordinary disasters here. This is not a book about stocking three days’ worth of canned goods and making sure the fire extinguishers are charged. With tongue tucked in cheek, Sheridan prepares for the proliferation of zombies, a new ice age and highly mechanized alien predators. He wears paranoia like a merit badge, reminding us, as a weightlifter tells him, that “comfort is the killer of the will.” And then he embarks on an odyssey of the sort of training that one might need if society imploded in grand Hollywood style.

There is, of course, fighting — fighting with fists and feet and knives and sticks and guns. But Sheridan, in real life an accomplished competitive martial artist, knows the reality of street fighting. He knows that the best street fight, the only street fight with a certain outcome, is the one that is avoided altogether. After all, a fight, even if won, will leave injuries, and in Sheridan’s dark future there will be no emergency rooms.

Which means that one should train for retreat. Get out there and do some track work, but forget about jogging. Joggers cannot outrun zombies. Sprint. Push yourself. Train your muscles for what they might actually have to do. And, while you still can, learn to start a car without a key. And then learn to drive it, at extremely high speeds, backward.

The catastrophic future is pure fantasy, but the training is real. In his zeal to learn, Sheridan — a Harvard graduate who has worked as a cowboy, farmhand, wildland firefighter and wilderness EMT — meets and works with experts in the skills that will come in handy when everything falls apart. He turns to reformed gangsters to hone his car-stealing skills. He takes driving lessons from a program intended for stuntmen. He visits a renowned wilderness school where students learn to deal with emergencies in the absence of ambulances and hospitals. He interviews a psychologist to learn how the mind will have to adjust.

What about food in Sheridan’s bleak future? He learns to hunt and trap. He learns to cook rat.

To cook, he needs fire. He discovers that starting a fire with a bow and drill is not so easy. It takes, he tells us, sweat and discipline and perseverance. In one case, he spends an entire day, under tutelage, in the quest for ignition. But this is important. In Sheridan’s future, matches may be a thing of the past.

He intersperses descriptions of training with glimpses of his imagined world, a few hundred italicized words at the beginning and end of every chapter, written in the present tense, each one reading like an excerpt from an apocalyptic novel. “Right before dawn is the best time for scavenging, the safest,” he tells us as he introduces a particularly horrifying alien invasion. In another passage, and another imagined future, he defends the family from a pack of cannibals. “With muted footfalls,” he writes, “the wraiths slip out of their holes. There are five of them, wrapped in black rags, with red-rimmed eyes, humanity long fled.”