The Alchemist, a class playable in the first Torchlight, becomes corrupted with Ember Blight and attacks the town of Torchlight a few years after the end of the original. The Ember Blight comes from the Heart of Ordrak (evil being that lived under the town of Torchlight during the first game) and the Alchemist is using its power to disturb the worlds balance.
The Hero then begins an adventure across three acts in an attempt to quell the disaster being caused by and that has become of the Alchemist.
Act 1 takes place in the fields of the Estherian Steppes. After the events of Act 1, you travel to a desert landscape named the Mana Wastes to begin Act 2. Act 3 takes you to the haunted forest of Grunnheim in search of the Alchemist.
