The climate change was a catalyst for a succession of events that led to the destruction of our world; rising sea levels have inundated the coasts. Only you can help humanity survive by leading your band of survivors on a path to redemption. Starting with a lost bunch of survivors, you need to scavenge resources, rediscover technology and maintain the peace between differing factions as you strive to rebuild society.
The world - as you know it - has gone, replaced by islands, swamps and isolated groups of survivors. Gathering scarce resources, you need to explore the world - island by island - helping those you can and dealing with those who do not share your vision of the future.
There's more to a city than just people. Food, shelter, water, health, security - the list is long and varied. Technology to be researched along a branching Tech-Tree, buildings upgraded and specialists to train. It's down to you to make sure all these needs are fulfilled; a job made all the harder with limited resources, space and labour to complete these tasks.
A society is only as good as its laws; it's up to you to define them. Will you usher in a new utopian age of equality or is your future a benign dictatorship? Not every group shares your vision and the choices you make can have a profound impact on the future of your settlement. A common goal will make your society more productive than one at loggerheads with itself; you need to define and choose your legal evolution and which route to follow on the Law-Tree but - as with all things - there are always consequences.
Each game is different; maps, events and make up of the world are randomly generated, allowing unique playthroughs every time.