With its tropical climate and glorious beaches Koh Samui is Thailand's fastest growing holiday destination.
Koh Samui staged a religious ceremony after Miss Horton's death
Just 20 years ago this island had neither electricity nor airport.
Now five-star resorts jostle for space along the shoreline with the budget accommodation so attractive to young travellers like Katherine Horton.
But her murder has drawn the world's attention to a darker side, far removed from the one seen by tourists hungry for new experiences.
This island's exotic attractions act as a magnet for nearly a million tourists every year and they spend £200m.
There's full employment on Koh Samui but now there are fears that this booming economy could be threatened.
As news of the New Year's Day killing of Katherine, 21, from Cardiff, made headlines, businesses began to feel the impact.
Her murder not only horrified Thais on the island, but also brought many anxious enquiries.
"We have some customers (who) get in touch with us and (ask) if they'll be all right if they come over to stay with us," Jack Dangsaard of The Spa hotel on the island told me.
A million tourists a year flock to the Thai island
There are just 15 tourist police on the island and a regular force of 200.
Hotels are now employing extra security guards to patrol the beaches. Women in particular are taking no risks.
British tourist Jane Charlesworth said: "I think I've always been aware and I think coming away on my own makes you feel more aware.
"The way I look at it is there are some horrendous things happening in the UK."
The new hut beach bungalows where Katherine stayed are still full of young travellers but the girl they never met is very much in their thoughts.
Martine Tempels, one of the travellers, told me: "It's something you can't really believe, like it's something that will happen really far away.
Katherine Horton was in the final year of a psychology degree
"But it's really close here, it really makes you think about it."
On Tuesday, as Miss Horton was laid to rest in her home city, thousands of miles away many islanders still felt shame that such a crime was committed here.
They want the death penalty enforced and on Wednesday her killers will learn their fate.
Miss Horton's mother Elizabeth has said she believes no one had the right to take another's life and wants the Thai fishermen who murdered her daughter to stay in prison until they die.
About 200 police officers were involved in the murder inquiry
She is satisfied with the pace of Thai justice. A Welshman on holiday here is not so sure.
Robi Dutta said: "It seems awfully quick to find two men very quickly and hang them very quickly. It's not really a kind of justice we're used to."
Murders are not unusual on Koh Samui although it's rare that the victim was a Westerner.
Holidaymakers, though, are targets for less serious crime - theft and robbery.
On Tuesday, the head of Thailand's tourist police will arrive on this island to discuss how best to protect visitors.
Already a government committee has recommended that CCTV is installed along these beaches in a bid to reassure tourists and restore this country's tarnished reputation, not just in Britain but across the world.