Geek couple Felicia Low-Jimenez and Adan Jimenez are 30 somethings who still find child-like joy in Lego toys, dolls, comic books, science-fiction movies and TV shows.

No wonder then, that children thrill to their Sherlock Sam food-themed mysteries. There are nine books in the ongoing series published by Epigram Books since 2013. More than 24,000 copies have been sold in Singapore.

The first four books in the series have just been picked up by United States publisher Andrews McMeel Publishing for sale in North America.

The books, illustrated by Singapore artist Andrew Tan or drewscape, are written for children aged eight to 12. They feature 10-year-old detective Samuel Tan Cher Lock, his robot sidekick Watson and a gang of friends who keep the ever-hungry Sherlock Sam in check.

"Sherlock is very smart, he's a genius, but he's easily distracted by food," says 32-year-old Jimenez, who read Nancy Drew mysteries while growing up in California and wanted to be a detective when he was a boy. The American citizen is a permanent resident here.

His wife is Singaporean. They married in 2012 and have no children. They both have a common cultural background: geekdom, or a deep interest in pop culture.

For the interview with The Straits Times, he turns up in a T-shirt hailing gamers and she wears one featuring Princess Leia of the Star Wars universe.

When this reporter interviewed them in 2013 for the launch of the Sherlock Sam series, they came armed with a magnifying glass and a deerstalker hat as a homage to the TV adaptations of Arthur Conan Doyle's Sherlock Holmes' mysteries.

Nothing thrills them more than seeing readers of their books "geek out" on Sherlock Sam in a similar way. They show off a photograph received from a boy who dressed as Sherlock Sam and posed with a cardboard model of Watson.

"We get these stories from parents who say their kids didn't like to read or were reluctant readers. Then they picked up Sherlock Sam and were hooked," Jimenez says.

"Even if it made a small difference, it means a lot to us," says Low-Jimenez.

Andrews McMeel Publishing has a gift for picking up titles that eventually become bestsellers. Its book list ranges from popular Tumblr poet Lang Leav for adults to the Big Nate series for middle-graders.

Ms Kirsty Melville, president and publisher for Andrews McMeel Publishing's book division, says in a statement that it is "thrilled" to introduce Sherlock Sam, a character already beloved in Singapore, to young readers in North America.

She adds: "His plucky smarts and spirited curiosity entertain in words and pictures to intrigue and delight readers."

Epigram Books receives a royalty or percentage of selling price on each copy sold - usually between eight and 12 per cent of the sales - and the authors get a percentage of that. Neither husband nor wife expect to become millionaires overnight, even though Andrews McMeel Publishing has the right to sell the Sherlock Sam books in the key markets of the US, Canada, Mexico and Central America.

Jimenez says: "It's more about the exposure and reaching new readers."

The series was the brainchild of Epigram Books founder Edmund Wee,who had brought out Singapore bestsellers such as Adeline Foo's The Diary Of Amos Lee series and wanted another set of books for the eight- to 12-year-old market here.

Low-Jimenez, 37, was then working at the company and her husband was the logical choice to write the new series. In 2012, he had co-written a choose-your own- adventure graphic novel, Twisted Journeys #22: Hero City, for American imprint Graphic Universe.

Low-Jimenez says: "What they gave us at the start was 'chubby boy detective Sherlock Sam who moves around Singapore'. The more we talked about it, though, the more I realised he wouldn't be able to write a local series."

So they pitched it as a joint project and have been working on it ever since. They are also co-writing a young adult novel, for which they received a grant from the National Arts Council, but have no plans to write full-time.

Both say they enjoy their day jobs. She is division manager of merchandising at Books Kinokuniya and he is assistant director at the National Book Development Council of Singapore.

Sherlock Sam is work but also play. Each book features a local food special - Peranakan dish ayam buah keluak in the first book, Sherlock Sam And The Missing Heirloom in Katong, for example. It may also show "hidden treasures" in different parts of Singapore.

Last year's Sherlock Sam And The Stolen Script In Balestier mentions the last free water kiosk on the island. A station for potable water in Boon Teck Road, it is still topped up regularly by volunteers from a nearby temple and dates back to the time when safe drinking water was hard to get in Singapore and much appreciated by weary coolies and rickshaw pullers.

"I've lived in the east coast of Singapore all my life so I get to discover and rediscover things about Singapore," says Low- Jimenez, who lives with her husband in an HDB flat in the east.

They walk together for research and work on an outline for the book before separating to write chapters turn by turn. They like to hide "surprises" for each other in the text, usually in the form of jokes or references to favourite comics or TV shows.

"If you hear the other person laughing, you know the joke worked, otherwise, you have to rewrite it," he says. "In the beginning, the editors knew which of us wrote which chapter, but we've gotten better now," she says.

In 2013, when the series debuted, they wrote four books. Now, they pen about three a year.

She compares their work on the books to a 3,000-piece Lego model of the Death Star, the moon-sized battle station featured in George Lucas' Star Wars universe.

They began work on the model one weekend afternoon and, by midnight, she decided to go to sleep. When she woke up hours later, her husband was putting the finishing touches on the Death Star.

"Usually, I start and he'll finish it," she says.