"You don't need to be an expert on the whole series of books," he reassured me.
"So long as you've at least read the first one you'll get a lot out of it."
However, those who sign up for the tour often have more than a passing acquaintance with the adventures of Precious Ramotswe, Mr JLB Matekoni, Mma Makutsi and the rest.
"If you don't get the details absolutely right, they're very quick to correct you.
"The Americans are the worst," he added as an afterthought.
It's hard to think of another writer who has so completely fashioned our view of a country as Alexander McCall Smith has with his No 1 Ladies' Detective Agency books.
According to the people I spoke to, it's a responsibility the author takes very seriously indeed.
This sense of responsibility is shared by Tim, who designed the tour.
"It's not just about showing people the places mentioned in the books; I also want the tour to introduce visitors to the land, culture, history and people of Botswana."
That said, every tour begins outside the house of Mma Ramotswe. A distinctive hallmark of the books is that McCall Smith tends to blend real people and places in Botswana with fictional ones, and the house he chose for Mma Ramotswe is the real house of friends of his, although the address is actually Zebra Way and not Zebra Drive.
It's a private house, so there was no admittance, but as we stood outside on the quiet street corner peering through the gate it was easy to imagine Mma Ramotswe sitting on her veranda after a hard day's crime-solving waiting for Mr JLB Matekoni to call.
Next stop was Mochudi, the village about 45 minutes' drive from Gaborone, where Precious grew up in the house of her beloved father, Obed Ramotswe. On the way, we crossed over the railway tracks at Pilane where Mma Ramotswe's mother died when she was hit by a train, the event "that had been the shadow across her life".
At Mochudi, Tim parked the four-wheel-drive by the kgolta, a thatched building open to the air on all four sides. Here the village chief and elders hold court on local matters as they have always done.
Across the dusty square stands the kraal where cattle are penned and which is the burial place of two local Bakgatla chiefs. Behind it is the austere-looking Dutch Reformed Church, where a young Precious Ramotswe stood on the steps on the arm of the dashing, but ultimately unreliable, Note Motoki, long before Mr JLB Matekoni appeared on the scene. And, in the village back streets, Tim showed me a typical house of the type Obed Ramotswe would have lived in after his years toiling in South African mines.
On the hill overlooking Mochudi stands the school the young Mma Ramotswe would have attended. Today it's a museum, which is happy to piggy-back off the success of the books to celebrate the local Bakgatla culture and tell the dramatic story of how they came to settle in the region.
Local artworks are produced on site and I bought a wall hanging of two women dancers "of traditional build", which was a snip at 120 pula (about NZ$20).
Later, back in Gaborone, Tim took me to Mma Ramotswe's favourite shop, the Botswana Book Centre, where, ironically, I couldn't find a single one of the No 1 books. Perhaps they were sold out.
And afterwards we drank redbush tea on the terrace of the President Hotel overlooking the market square, one of Mma Ramotswe's favourite haunts.
On day two, Tim handed me over to his assistant Bianca, whose knowledge of the McCall Smith books was no less extensive.
She drove me along the Tlokweng Rd, but sadly there was no Speedy Motors to be found or tiny white van for that matter.
However, there were a couple of garages that could have passed easily for Mr JLB Matekoni's thriving business. Mechanics in greasy overalls laboured under the bonnets of assorted cars and trucks, the ting, ting, ting of their hammers echoing the sound of the cow bells I had heard the day before standing outside the school in Mochudi. Every morning, everyone in the country awakens to the sound of cow bells on Radio Botswana.
Next we drove past the Old Defence Club before parking outside Mr JLB Matekoni's house, another real location that belongs to friends of the author.
Motshwari Kitso is the head of SOS Botswana, to give the "orphan farm" of the books its real name, and the morning we visited him he was not a happy man.
Apparently, a tour operator had featured the orphanage in one of its advertisements.
The books have been a great benefit to the orphanage and have helped attract volunteers and raise awareness and much-needed funds. A visit to the orphanage is part of the itinerary. But "orphan tourism" it is not.
"People are welcome," Motshwari told me, "to contribute to our work in any way they can - ideas, suggestions, not just money."
Most of the children were at school that morning, but the smaller ones seemed happy to see us and rushed up to shake our hands, before running away squealing.
The Mokolodi Nature Reserve has been another beneficiary of the books. Here I met Neil Whitson, who runs it as an education centre to teach local children about wildlife and conservation.
Neil is a tall, tough-as-nails South African who pops up in book number seven, Blue Shoes and Happiness, and makes his introduction by walking into Mma Ramotswe's office and calmly picking up a snake that has been terrifying her.
As Neil told me in his gravelly South African drawl how the books have helped revitalise the game reserve, I thought he belonged more in the pages of a Wilbur Smith novel rather than a McCall Smith one.
Chances are even the most die-hard fan isn't going to come all the way to Botswana and visit only Gaborone. Most people go up to the Chobe National Park but instead I headed off to the Moremi Game Reserve on the edge of the Okavango Delta. It was a 30-minute flight in a four-seater Cessna.
In Moremi, I stayed at the Xakanaxa Camp, a luxurious Eden of 12 safari tents in the heart of the wilderness.
As well as going on game drives, you can get out on the water and explore the fringes of the delta, either by motor boat or in a traditional mokoro, a small wooden boat punted with a pole, gondola-style, through the shallow waters.
The real excitement of the mokoro, though, is that it is low in the water and brings you eyeball to eyeball with hippos and crocodiles.
So far, Mma Ramotswe hasn't made it to the Okavango Delta, but when a case does take her out of Gaborone it's often into the wilds of the Kalahari desert. So my next stop was Deception Valley Lodge in the Central Kalahari Game Reserve, where my guides were Adrian, a blond South African, and Nimzi, a San bushman who, standing on his toes wouldn't come up to Adrian's armpit.
Each morning we rose before the sun at 5.30am for a game drive, spotting giraffe, kudu, water buffalo, impala, emu, springbok, oryx and, on one occasion, the flash of a black mamba disappearing into the scrub. This being the wet season, the Kalahari was carpeted with grasslands and trees that mushroomed out of the fine white sands.
On evening game drives, a waterhole close to the lodge practically guaranteed us a sighting of lions, a pride of eight adults stretched out in the setting sun.
"The Kalahari lion is the biggest in the world," Adrian told our small group in hushed tones.
As if on cue one of the males rose to his full height and sauntered over to drink at the waterhole. I swear I've seen smaller horses. The next day we saw them prowling around the airstrip.
It was lucky there were no light aircraft due that day - the lions had left half a wildebeest in the middle of the runway - but the most magical sighting was of a young female leopard that walked so close to our open-top four-wheel drive that I could have reached down and patted her on the head.
On our final evening, Nimzi took over and escorted us on a three-hour walk through the bush. As the sun set, streaking the sky with purple and gold, he showed us the traditional way of life of the Kalahari bushmen. How they made poison for hunting, tracked game, found water, trapped birds and eked out an existence in one of the last great wildernesses on earth.
Carrying all his worldly possessions in the dried skin of an impala, and with Adrian translating his strange language of clicks, this elfin man, dressed in no more than a strip of animal hide, showed us a range of survival skills that made the SAS look like a troop of boy scouts.
But Botswana is changing.
Back in the capital, at the Gaborone Sun hotel and casino, beautiful girls dealt cards at blackjack tables from three-deck shoes with all the dexterity of their Las Vegas counterparts.
Meanwhile, Botswana's bourgeoisie fed the slot machines with metronomic enthusiasm.
When Botswana won independence from Britain in 1966, it was listed as one of the 10 poorest countries in the world. But independence coincided with the discovery of diamonds and, today, Botswana produces 60 per cent of the world's gem diamonds.
Thanks to good governance, a lot of that wealth ends up not in the Swiss bank accounts of corrupt politicians but staying in the country, where it provides universal education, healthcare and even state pensions.
In many ways, Botswana is a showcase of what Africa can be and deserves to be.
No one understands this better, I suspect, than McCall Smith himself, who I'm sure recognises that the fragile customs and ways of life that are the real stars of his No 1 Ladies' Detective Agency books may not survive the onslaught of development.
Where this will leave Nimzi's way of life is anyone's guess. Hopefully the San people won't be completely eclipsed by the Sun Casino people.
As Mma Ramotswe might say, time in Botswana right now is precious.
CHECKLIST
What to do: Take Africa Insight's official No 1 Ladies Detective Agency Tour.
For bespoke Botswana safaris, see africanexplorations.com.
Bob Maddams travelled with African and Indian Explorations.
- OBSERVER
