The scene is set in the wilds of southern Cambodia. Creepers dangle from meranti trees, the wide waters of the Prek Toeuk Sap estuary sparkle, and glades are spotlighted by the sun. The lead actors, however - the rhesus monkeys, Malayan sun bears and Irrawaddy dolphins who were supposed to perform for my benefit - have missed their cues. When it comes to nature-watching, patience is the only virtue.
I'm on a long-tail boat in Ream National Park, puttering through miles of mangrove at a petrol-conserving pace. The driver explains that not only do these trees have a matrix of roots that protects the shoreline by breaking up currents, they provide everything from fuel and building materials to paper and perfume. A shy young man with a connection to nature not shared by this boatful of townies, he's constantly grabbing waxy leaves, pointing out how this one can treat neuralgia, while that one will cure haemorrhoids. What do we eat for such problems in our homes? Tablets, we tell him.
Informative though all this is, what we really want to see are the monkeys. I scan the undergrowth, hoping for a crab-eating macaque to emerge, perhaps pursued by a clouded leopard (unlikely, but both survive out here in the 37,000 acres of greenery). However, there is nothing but the chugging of the engine, the lapping of the water and the quietly soporific tree-scape.
Cambodia's environment wasn't always so carefully tended. The chaos of the Khmer Rouge era placed a great strain on the country's resources, and any saleable land was logged. When King Sihanouk was reinstated in 1993, he countered deforestation by designating seven conservation parks and 10 reserves. Today, an impressive 18 per cent of the country is protected by royal decree, a figure that compares favourably with the 7.6 per cent dedicated to national parks in England.
Still without a monkey sighting, we pull in where the estuary meets the Gulf of Thailand for a lunch of steamed barracuda. Stilted shacks perch on the beach. One of the children shows me a new trick: how to treat a burn by scraping the powdery surface of a piece of cuttlebone. It's more evidence of an easy affinity with nature of which I'm both admiring and envious.
On the way back, we finally encounter some wildlife: a kingfisher furiously chases tiny flying fish; an otter pops its head up; a greater adjutant with long trailing legs and a six-foot wingspan glides overhead. Still no monkeys, but an altogether wilder experience is promised at the neighbouring national park of Bokor.
Getting there from my tastefully appointed cabin in Sihanoukville, Cambodia's leading beach resort, proves difficult. Despite the ubiquitous moto touts, when I actually want a taxi it's hard to commandeer one. Eventually a driver is persuaded to head down Route 3 towards the Elephant Mountains. With the sun setting behind us, we tank through luminous rice fields, every glance out of the window returning a snapshot of the poverty and vitality of rural life: children riding water buffalo, families of five squeezed onto Honda Dreams, a gardener cutting the grass of a hotel lawn with a sickle, four girls in gold lamé outfits miming on a makeshift stage. Everyone is busy.
Transport is the great leveller in Cambodia. So far I'd managed to avoid the roads, arriving from the Thai border on a sleek speedboat and then sticking to the waterways of Ream. Now, as darkness descends and our rear left wheel inevitably blows on the gravel, I'm reminded of an agonising trip I once made along Route 6, covering 50 miles in 15 hours. Now, on this remote stretch of unmade road, devoid of street lighting, markings or signs, rusting trucks without headlights veer around us as we struggle to change the wheel by starlight. I can see why the driver was reluctant.
Next morning, there's more rough riding as I corkscrew up Mount Bokor in a battered Toyota Camry belonging to Samlain, a park ranger with a 350,000-acre job on his hands. The track bears every hallmark of landslides, torrential rainfall and zero maintenance; despite the Toyota's raised suspension, we're thrown from side to side.
Despite the arduous progress, there's a sense of being swallowed as the trees close in around us, huge yellow butterflies flickering like sparks in the gloom. Peering up at the canopy, I spot a mammal with a long tail: a giant black squirrel. Suddenly I fancy my chances of seeing some proper wildlife, so we find the nearest trail and plunge behind the trees.
Like almost everyone else I've met in Cambodia, Samlain is completely at ease amid an abundance of flora. While I'm falling over tree roots, he's tipping the water from a pitcher plant to reveal the luckless insects inside, pointing out a clump of Venus flytraps, cautioning me about the points on a serrated palm and sharing a cure for diarrhoea (eat seven guava leaves). We crack a fistful of tamarind husks, and nibble the leaves of an edible fern. We even find wild aloe vera. Left to our own devices up here, it's abundantly clear which of us would survive.
Tramping back, Samlain is telling me about the week-long forays he's made into the deeper forest. Has he ever seen an elephant? "They're easy to find," he says. "You just cut down a big tree, the elephant hears the boom and comes along to eat the sweet leaves from the treetop." I make a mental note in case I ever need an elephant in a hurry.
Suddenly there's such a crash that I imagine a parachutist has strayed into the trees, but then the biggest bird I've ever seen is descending ahead of us, successive branches snapping under its weight. A curved beak bigger than its body, protruding from a yellow casque, crunches back some kind of nut. Then the hornbill (as I find out later) flaps away in an ungainly flurry of black wings and claws.
Our second bird encounter, though we never see it, is more significant. It's a type that feeds on whatever tigers leave behind, and Samlain freezes when we hear its piercing peep-peep: it means a tiger is likely to be nearby. Several long minutes later the call fades and the tiger, if it was ever there, is gone. Although I'm disappointed, seeing it would have been a privilege I hardly deserve: in five years as a ranger, Samlain has sighted only one tiger.
We continue to the summit to enjoy a misty view of the Vietnamese coast, and to visit the plateau where the blackened shell of the Bokor Palace Hotel and Casino still smoulders. Once the playground of French colonialists, later occupied by Vietnamese soldiers, the walls of this grand structure are now a mosaic of soft red lichen, bullet holes and graffiti. Our accommodation is a large and cosy bunk bed at the far more practical National Park Research and Training Facility. As night falls, above the sawmill screech of countless insects I can make out the faint whistling of a female gibbon, mocking my failure to find a single primate.
When I get back to Sihanoukville next day, there on the roof of my cabin, wearing a "where have you been?" expression, is a rhesus monkey.
There are no direct flights to Phnom Penh from the UK. Thai Airways (0870 606 0911; www.thaiairways.co.uk) flies from Heathrow via Bangkok and Malaysia Airlines (0870 607 9090; www.malaysiaairlines.com) flies via Kuala Lumpur, also from Heathrow. Faraway Traveller (01435 873666; www.farawaytraveller.co.uk) offers return fares from Heathrow via Kuala Lumpur for around £550 with Malaysian Airlines.
Most hotels insist on US dollars. The international-standard Crystal Hotel in Sihanoukville (00 855 3493 3523) is close to Ochheuteal beach. Doubles start at $35 (£19), including breakfast.
In Kampot (for Bokor National Park) try the colonial Bokor Mountain Lodge (00 855 3393 2314; www.bokorlodge.com). Doubles start at $33 (£18), including breakfast. The best budget choice is the western-run Blissful Guesthouse (00 855 1251 3024; e-mail: firstname.lastname@example.org). Rooms start at $4 (£2.20), room only.
Sok Lim Tours (00 855 1271 9872; www.soklimtours.com) arranges package and custom tours to the national parks and other local attractions.
British passport-holders require a visa. One-month tourist visas can be obtained on arrival at Phnom Penh and Siem Reap airports and some border points for US$20 (£11). The Cambodian Ministry of Foreign Affairs has launched an e-Visa facility for tourists, with an additional US$5 (£3.60) processing charge; apply via the website: www.mfaic.gov.kh