We’ve all heard about the Japanese soldier who, after the second world war ended, stayed on the Philippine jungle island where he was stationed, armed and lethal, dismissing all signs that Japan had been defeated as enemy propaganda. His name was Hiroo Onoda; he finally stood down in 1974 after almost 30 years of delusional guerrilla warfare and died in 2014. Werner Herzog, the prolific German film-maker who narrates his documentaries in a Wagnerian register (wonderfully parodied in the YouTube video Werner Herzog Reads Where’s Waldo?), contrived to meet Onoda in 1997 and has now written a very short, only partially satisfying book about him. The Twilight World is best described as a nonfiction account of Onoda’s long, pointless mission that phases in and out of fiction – or vice versa.

So why didn’t Herzog do the obvious thing and make a film about Onoda instead? Perhaps because another film-maker got there first: Arthur Harari, whose impressive feature Onoda: 10,000 Nights in the Jungle has recently been released. Stretches of The Twilight World read like a screenplay or documentary outline that’s been injected with prose fiction growth hormones. In the expository and digressive passages, it’s impossible not to hear Herzog’s famous voice ringing charismatically in the inner ear (just as that of Quentin Tarantino resounded unmistakably in his recent novelisation Once Upon a Time in Hollywood). If a less celebrated figure than Herzog presented their editor with a book this slight, they’d probably be sent back to their desk to imagine their way deeper into the psychic jungle, fleshing it out with a few more chapters. Which is to say: we’re here for the writer as much as for the story.

This isn’t Herzog’s first book — he is the author, most notably, of the 1978 travel diary Of Walking in Ice – but they’re rare enough to invite the question we always ask when a lauded artist switches lanes: will he make a tit of himself? The start is shaky – if they ever award a prize for ropiest opening lines, my money is on Herzog (and his translator Michael Hofmann): “The night coils in fever dreams. No sooner awake than with an awful shudder, the landscape reveals itself as a durable daytime version of the same nightmare, crackling and flickering like loosely connected neon tubes.” Happily, this hallucinatory nonsense is a false alarm: the prose soon settles into a less hysterical descriptiveness, with only the odd surreal apocalyptic flourish. The author wisely trusts in the story he’s telling – and with one this good, he can well afford to move out of the way.

In 1944, young intelligence officer Onoda is sent by his superior Major Taniguchi to Lubang Island with orders to destroy an airstrip, undermine the enemy American forces with guerrilla attacks and await the triumphant return of the imperial army – a mission he will cleave to for three decades with dizzying literal-mindedness. Taniguchi tells Onoda: “Your base of operations will be the jungle. Your campaign will be one of attrition. Skirmishes, ambushes, unpredictable attacks. You will be like a ghost, elusive, a continuing nightmare to the enemy. Your war will be without glory.” With three men at his command – the last of whom will be killed in the jungle in 1972, two years before Onoda surrenders – the soldier first engages the US forces in combat and then, after they leave, commences his absurd, prolonged resistance to a vanished adversary.

In Herzog’s account, Onoda’s war assumes the glitchy, totalising paranoia of a Philip K Dick novel. With elegantly insane anti-logic, he interprets all evidence that the war is over as proof of the contrary. Newspapers, leaflets dropped over the jungle from aircraft, radio broadcasts and even pornography are deemed intricate forgeries designed to trick him into surrendering. Characteristically, Herzog envisions Onoda as a kind of existential hero – his mission obscure, his trials unknown, his enemy vast and metaphysical. Existence and combat are one: “Every human being on this island is my enemy.” Onoda is also, of course, a bizarre excrescence of imperial Japan, whose pressure-cooker code of duty, honour and sacrifice he takes to self-negating extremes.

In its brevity, The Twilight World is sometimes as superficial as a Wikipedia entry – whole decades are skimmed over in a line or two – and at times frustratingly withholding. Herzog informs us that “the matter of those he had killed among the population never quite went away”, but no deeper investigation or reimagining follows. A bit of Googling reveals that Onoda and his comrades may have murdered as many as 30 people during his three decades as a rogue commando – which would make him one of the 20th century’s weirdest serial killers. The Twilight World provokes – and thwarts – an appetite to know more. Nearing his 80th birthday, Herzog gives off the megalomaniacal vibe of one who won’t let old age slow him down, perhaps won’t even notice that it’s happening. I hope he follows up this book with a probing, feverish and apocalyptic documentary: Hiroo Onoda – Human War.

• The Twilight World by Werner Herzog (translated by Michael Hofmann) is published by Bodley Head (£14.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply