By the time a terminal glare from my wife silences my efforts at a David Niven accent, it is too late. The gangplank has not yet been pulled on board, but in the wood-lined 1930s-saloon of the SS Sudan, we have already fallen through time. The ship is 130 years old, ancient Egypt's treasures lay downriver and the waiters have been compelled to wear a fez as part of their uniform.

On the wall are black and white photographs of a glowering King Farouk on his wedding day, in 1938. Wilfully dated lamps illuminate brass fire extinguishers, an antique globe and some well-worn drinks tables while 12 copies of Death on the Nile, in English and French, pad out the small library's shelves. This is, after all, a former royal paddle steamer and original Thomas Cook tourist boat, as well as the ship that carried Agatha Christie up the Nile to inspire one of her - and her fictional detective, Hercule Poirot's - most famous outings.

When we booked the trip, I congratulated myself that foresight had yielded the Hercule Poirot room - surely, I felt, the prime cabin for any right-thinking person making this voyage. As we emerge on the first morning, however, we discover fortune may not have played much of a role, after all. There are only five guests on board: a French couple, my American wife, an older German lady who doesn't want to set foot off the ship until journey's end, in Luxor, and I. None of us is bilingual and all appear quite content to be subsumed by the sleepy creakiness of the boat. If a murder is going to happen on this voyage, the detective is going to need a small room and more than one phrasebook.

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The ship sets off from Aswan after a quiet breakfast in the grand but near-empty dining room. It appears the chef has prepared his kitchen for a voyage with considerably more passengers, and so is applying a "bake it and they will eat" philosophy that has mainly skewered the one person too British to say "no". I smother lots of Egyptian bread with copious amounts of black honey.

If the decadence of this trip isn't exaggerated enough by the flutes of hibiscus tea and cold towels that await our every return to the ship, then the knowledge that we are floating down the Nile with five eager staff members to every tourist certainly finishes the job.

We stop first at the temple of Kom Ombo, replete with its mummified crocodiles dedicated to the god Sobek. The pattern for these twice-daily stops is quickly established, our guide providing a well-practised rundown of history, beliefs and the pantheon of Egyptian gods, followed by time to pick our own lazy way between the columns and hieroglyphics.

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On a trip that seems so rooted in an earlier era, the constant bass note is the backdrop of temples and monuments. While on the river, the SS Sudan draws us into a 1930s world, our stops deliver us to somewhere outside of time itself. We arrive in a boat that has carried tourists for well over 100 years, but that is only a recent period in a grand tradition of wide-eyed travellers who have visited and graffitied these places for a millennium.

By the second morning, the rhythmic thumping of the paddles against the water has thrummed our brains into a slower state of mind. The trip can be done in a day on other tourist boats, but as the oldest ship doing the run, and the only one still doing it by steam, the ponderous three days our journey takes makes us feel like we are drifting on the current. As the ice cracks and melts in our G&Ts, and the French lady hums quietly to herself from a lounger across the deck, the thin green strip of life around the Nile steadily unravels around us. We read, we doze, we stare at the scenery.

Death on the Nile is a tragic upper-crust love story set amid Egypt's historical highlights. In the novel, there is a brooding sense that this small group of well-to-do travellers, variously bored and fascinated by the hot, dusty sites they are visiting, are very much isolated on this doomed chunk of empire floating down a river far from home. Nearly all of the characters seem poised on the brink of madness. By the end of the story, five of the 13 or so main characters have died and dear old Poirot can only ruminate on the power women can wield. Watching the scenery glide by as Christie herself did from this ship - although she headed south from Aswan, to Wadi Halfa - I can see how the pace, the late summer heat and the punctuations of relics from a grand age would have inspired such a story.

Our own little band of travellers are - outwardly at least - more stable. If there is a comparable undercurrent of something darker, it is only in the scarcity of tourists at each of the places we visit. By virtue of our numbers, both couples have already been assigned their own guide and separate transport, while at each stop we are rarely competing with more than a couple of other tourists. Even the anticipated throngs of hawkers selling tourist tat are decidedly threadbare, leaving only relaxed and well-armed tourist police to provide any real sense that the places are even open.

Recent random attacks and bombings have prompted even Egyptian friends to suggest this might not be the best time to visit. Contrariness and non-refundable deposits stayed our hand, though, and it feels like we made the right choice. Nowhere on our trip feels threatening or unsafe and, while it never entirely leaves our thoughts, it is only amid the slightly larger crowds in Luxor that we dwell on the suggested threat.

On the final night, the waiters bring out a projector screen and we all sit down to watch the 1978 film version of Death on the Nile. I note that my Niven impression was spot on, and his character's exasperated, "Damn it man, can't you speak a language we all understand?" could well have been addressed to our present company.

As the film ends, the French couple nod politely and the German lady chuckles over the credits. We all quietly head to bed in our isolated cabins on this empty boat, our own Death on the Nile ending rather more gently than the film.

Getting there: Etihad flies from Hong Kong to Abu Dhabi, and from there to Cairo. EgyptAir operates a regular service from the Egyptian capital to Aswan.