By Stephen Gibbs
BBC News, Cancun
Cancun is one of Mexico's major tourist resorts
To most of its four million visitors a year, Cancun is blue sky, turquoise sea, white sand, and huge all-inclusive hotels.
The sort of place where the drinks flow freely, and the troubles of the world seem a long way away.
But venture into downtown Cancun, a few kilometres from the beachfront, and it's a different story. Here, the troubles of modern Mexico are there for all to see.
Army patrols rumble through the streets. The city's special police forces disguise themselves with ski masks and dark glasses for fear of retribution. If the mayor steps out of his office, he is flanked by bodyguards.
Geographical accident gave Cancun its perfect weather and spectacular coastline. It also provided the ideal staging post for drugs on their way from South America to the United States.
With the added bonus of a few thousand consumers, in the form of tourists, on site, it is easy to see why the city is the jewel in the crown for Mexican drug traffickers. The battle for its control is brutally fought.
On 1 February, retired Brigadier General Mauro Tello Quinones arrived in the city.
The former commander of the army in the western Mexican state of Michoacan had a powerful reputation as a man of war; someone who could fix any problem. He had been personally invited by the recently elected mayor, Gregorio Sanchez.
The army has been carrying out checks in and around Cancun
Gen Tello's task was to weed out corruption in the city's police force; to take back the streets from criminal gangs.
He lasted less than three days at work. On 3 February, together with his bodyguard and driver, he was abducted. The three men were tortured and then driven to a remote jungle location where they were killed with a bullet to the head.
As we met in his offices, the charismatic Mayor Sanchez appears a man undaunted. Remarkable, given the fact that he had not just lost an ally, but his family had suffered a tragedy too.
The mayor's nephew was driving the general that day.
"We need to put fear behind us, and show them what we are made of," he says, striking the table with his hand. "The people chose us as leaders. We need to act that way. With character, with courage, and with determination."
The general's murder led to a immediate and dramatic shake up of the Cancun police force.
The following day the army swooped on the local station, purportedly checking arms licences. They left with the police chief.
Francisco Velasco Delgado, known as the "Viking", has since been accused of working in league with a drug cartel hit squad.
The military has made its presence felt. On the main motorway between the resort of Playa del Carmen and Cancun, marines set up a checkpoint, searching cars for weapons or drugs. The police watch from a distance.
"I have no problem with it," said a Brazilian tourist, as he was forced to climb out of a taxi whilst two soldiers searched the vehicle. "They are just doing their job."
But some fear that the tendency of the Mexican government to hand over law and order responsibility to the army, albeit temporarily, is dangerous.
Mexico's Commission for the Defence and Promotion of Human Rights (CMDPDH) says that currently 11 out of Mexico's 31 states are policed by the army.
"I think the government should be really careful," says the organisation's director, Paulina Vega. "During these operations many civilians have been caught in human rights violations. We have the army taking care of security, but no accountability once abuses happen."
Cautious voices such as hers are up against much louder demands that something, anything, must be done to stop Mexico's spiralling violence.
"If we want a clean country, we have to do whatever we have to do," says Javier Ibarrola, a security analyst with close links to the Mexican army. "Fight? OK...we have to solve this problem now."
There were more than 5,000 drug-related deaths in Mexico in 2008
On the streets of Cancun, I spend a couple of hours on patrol with a recently created new division of the local police force, the Fepa.
Its officers are more vigorously vetted, and better paid than the regular police. They work very closely with the army, and are on the front line of operations against organised crime.
We travel in a black Hummer. The driver is completely disguised with helmet, mask and goggles. Even his colleagues at the police station don't know who he is.
Perhaps surprisingly, he is a thoughtful, eloquent man.
He says he wants to see a more peaceful, secure Mexico before he dies.
"But the problem is growing all the time," he adds.
I ask him why. His reply is blunt: "More people need the drugs."