The world was going to hell, and it was all my fault.

For six months I’d been working as part of a team fighting deadly disease outbreaks around the globe. Things hadn’t gone entirely to plan, and now the virulent strain of flu that had swept through much of Asia had hopped the Pacific to establish a foothold on the US west coast. To make matters worse, outbreaks of a highly contagious fever in Latin America had led to widespread civil unrest, making travel in the region hazardous. And as for sub-Saharan Africa, it was starting to look like there was nothing we could do to save it from complete and catastrophic collapse.

That’s the kind of apocalyptic scenario that awaits players in Pandemic Legacy. A successor to the hit 2008 board game Pandemic, it casts players as a team of doctors and scientists criss-crossing the globe in an attempt to prevent four deadly diseases from wiping out humanity.

This new interpretation retains many of the elements that have made its predecessor a favourite. Based around an ingenious system of chain reactions, where outbreaks spread rapidly and unpredictably across a web of interconnected cities, it packs a steadily increasing difficulty curve and an air of tension that ramps up in intensity with each successive turn. But this new version also adds something else to the mix: an ongoing storyline that develops over the course of multiple plays.

Each game session represents one month of what co-designer Matt Leacock understatedly calls “a very bad year for humanity”, and every month brings with it a new set of threats, challenges and mission objectives you’ll have to complete if you hope to hold back the tide of contagion.

This is relatively new ground for tabletop gaming, where most games are designed to be played in one-off sessions. But while the concept is novel, it’s much more than a novelty, and the game goes to great lengths to put its storyline front and centre.

It comes with a set of black boxes which you’ll be instructed to open at crucial points in the unfolding narrative, and each contains new chips, tokens and other elements to add to the game, fundamentally changing the way you play like some sadistic, smallpox-infected advent calendar.

That’s just one facet of the game’s complex, evolving narrative, though. While the major events of the plot occur at predetermined intervals, the choices you make in your efforts to halt the ever-advancing plague also have lasting effects. Allow cities to be hit by repeated outbreaks and they’ll start to unravel as panicked citizens riot in the streets. Let the situation deteriorate and they’ll turn on the very people trying to save them, torching your research centres, blocking your attempts to travel through the region and seriously undermining your efforts to treat the infected.

The worst thing about this social disintegration is that it’s permanent. You’ll affix stickers to the board indicating when cities have descended into anarchy, and the consequences of your decisions will follow you from one game to the next. With more simultaneous crises popping up than you ever have the resources to deal with, it’s impossible to prevent disorder, and the best you can hope to do is manage and contain it.

You’ll also have access to a cast of characters, each with their own special abilities. Some specialise in treating outbreaks, clearing cities of infection at lightning speed, while others excel at research, quickly developing cures to diseases – and choosing the right team to field in response to any given situation is a tough decision in itself. Your team will also gain experience as the campaign progresses, picking up new skills, developing relationships with team-mates and becoming steadily more useful in the face of an ever-increasing threat level.

This continuing growth gives characters a real sense of identity, and it’s difficult not to develop an attachment to them – not least because you’ll have a chance to name them before sending them into the fray, writing their details on a passport-style record book. But there’s also a horrible flip-side. Characters present in a city when an outbreak occurs suffer a variety of psychological scars, restricting their actions in the game. Repeated damage eventually leads to characters becoming “lost”. Deserted? Incapacitated? Dead? The game never makes it explicitly clear, but whatever the case, they’re gone, and they’re not coming back.

All of this means that no two groups will ever have quite the same experience playing Pandemic Legacy. You’ll create a world that’s unique to your copy of the game, and it’s up to you to choose the upgrades and strategies that will best help you deal with the mess you’ve made of the planet.

This all adds up to an extraordinary triumph of design, not just as a game, but as a piece of episodic storytelling. Each play-through feels like an episode of a big-budget HBO series, and the urge to binge your way through multiple sessions can be hard to resist. There are shocks, twists, cliffhangers and interpersonal drama, and you’re likely to find yourself dwelling between games on mistakes you made in your last session and making plans to deal with newly revealed threats.

The one downside to all of this is that you’ll only be able to play the game a finite number of times – anywhere from 12 to 24 depending on how well you do. This might be off-putting to some, but it shouldn’t be. Nobody complains about a novel because it ends. No one avoids going to the movies because films inevitably come to a final act. The game’s limited lifespan is what makes it meaningful. Yes, it’s fun. Yes, it’s challenging. But more than that, it’s a narrative engine designed to create unforgettable moments and batter you with a constant stream of emotional highs and lows.

You’ll suffer agonising losses in games that seemed to be going your way. You’ll pull out incredible against-all-odds victories through combinations of luck and clever play. And when it’s all over, you’ll end up with an experience and a set of memories truly unique to you and your friends.

The subtitle on the game’s box reads: “Season One.” Sign me up for season two – this may be the best board game ever created.

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