Adding zombies to anything immediately makes it better. That's not an opinion. It's a bona fide, irrefutable fact. So, while the cynics might think that cramming the slavering undead into Red Dead Redemption's latest DLC is nothing more than a simple exercise in making everyone sit up and pay attention, you'd be partially right, but you'd also be missing the point entirely. Yes, this is Red Dead with zombies, but it's potentially much more besides.

Undead Nightmare begins at Marston's family homestead in Beecher's Hope, where there follows an overnight zombie epidemic, which sweeps the entire frontier. Spurred on to track down a cure, Marston leaves to venture once more into Red Dead's sprawling sandbox world, which has been completely infected. None of the prairies, plains, forests and settlements have been spared from the spread of the zombie virus, so people and animals alike have been transformed into the mindless brain-munching undead.

Beginning at The Old Bacchus Place, our demo opened with John finding toothless grave robber Seth attempting to play a hand of cards with a zombified Moses by the riverside. The cutscene is an edgy one as it looks like Moses could turn on Seth and Marston at any time, so when we're told to leave and visit the first of five graveyard plots - that effectively now act as Undead Nightmare's gang hideouts – it's a welcome relief. Embarking upon the first mission, we gallop off on Marston's newly acquired zombie horse to a graveyard in Sepulcro, where we need to burn coffins with a torch (which also doubles as a melee weapon). Lighting up the creaking old wooden caskets prompts the zombie hordes to attack on sight, making torching the other exhumed coffins a challenge as you fend off waves of reanimated corpses.

Ammunition is pretty scarce, which makes these kinds of encounters more intense as we quickly learn. These are no shambling zombies, as we're set upon by scuttling Bolters that pounce from all-fours with terrifying speed and agility, as well as the more traditional, slower zombies and large Bruisers that charge without warning, sending Marston flying to the ground. Mercifully, there are none of Undead Nightmare's exploding, projectile vomiting Retchers at this particular juncture. They're saved for the later encounters.

You'll immediately find that the new Blunderbuss weapon is your best friend in almost every situation as it can be packed with any and all zombie bits you find when you harvest their splattered, decaying remains. Marston still has access to his standard cache of weapons, and indeed the shotguns, rifles and revolvers are still as reliable as ever, but the Blunderbuss is a devastating one-shot kill that can take out several zombies in a single, massive blast. It's slow to reload, with a whole animation that has Marston using a ramrod to stuff zombie eyeballs, ribs and other undead detritus down the barrel, but thankfully, you have an improved melee attack at your disposal, meaning that Marston will beat away enemies with the butt of a weapon, without hesitation.

Once the graveyard is cleared and all the coffins are burnt, a familiar face rises from a marked grave, and it's someone you might remember from one of the stranger missions in Red Dead's main storyline – the melancholy Miss Horlick. Upon dealing with her and the remaining undead, the perpetual gloom lifts, the weather in the immediate area improves and the zombie population is temporarily reduced. Chalk one up for Marston and the rest of humanity.

Saddling up onto our undead steed once again, we forge onwards to Ridgewood Farm to clear out the settlement and rescue a survivor for one of Undead Nightmare's many Missing Person missions. Along the way, the zombie horse's disobedient nature becomes apparent as letting go of the analogue stick for even a split second causes the rotting nag to stray off course, but then its higher stamina and top speed more than makes up for this slight inconvenience. Arriving at the farm after some slight horse wrangling en route, we set to work on the barn, where a lone gun man is besieged by a gang of zombies. We've inadvertently stumbled upon one of many ambient challenges here, which involves giving the trapped cowpoke some shotgun shells to help him survive. We soon locate the person we're looking for who runs towards us, actively looking for help making him eager to saddle up and ride out with us. After a quick journey, we get the survivor back to Undead Nightmare's only 'Clean Zone' at Fort Mercer, where you can choose to rescue another survivor by tearing down a designated Missing Persons poster.

The final part of the hands-on demo takes us to Rathskeller Fork, where we're given the seemingly simple task of clearing out the marauding undead element to gain a safehouse for Marston. Eradicating zombies from any settlement like this – as denoted by a progress bar at the top of the screen – grants you with a place to save your game and rest up. Scrabbling to a rooftop with a Gatling gun, we take the time to try out some Zombie Bait, Boom Bait and Holy Water to thin the crowds. Each is a new zombie-slaying projectile, invaluable for wiping out larger groups, but the bait proves to be the perfect tool to enable Marston to get the zombies all in one spot so that they can be torn to shreds with the Gatling gun. Cleaning up the remnants with some undead flesh-burning Holy Water, we take the settlement back, gain a safehouse and the demo ends.

We've had only a brief taste of what Undead Nightmare has to offer with its five new weapons – Torch, Blunderbuss, Boom Bait, Zombie Bait and Holy Water – zombie horses, a random zombie cow and hundreds of ravenous decaying humans. Amazingly, the entire game appears to have been transformed, from the sickly red and yellow interface to a brand new eerie soundtrack, recorded by original composers Bill Elm and Woody Jackson, and the hanging darkness that pervades every square inch of Red Dead's vast open-world. One thing is for sure, it looks like Undead Nightmare is going to be a truly indispensable add-on and that's without even mentioning the next part of the DLC, which we'll be covering in a follow-up preview next week. Oooohh, secrets!

Red Dead Redemption Undead Nightmare is coming to the PSN on October 26th for $9.99.