Mini Series is the first five episodes of Season 1 of Transformers: Prime.
The series begins with a five-part story called "Darkness Rising". In Jasper, Nevada, three young humans - Jack Darby, Miko Nakadai, and Rafael Esquivel - are accidentally caught in the crossfire in a fight between enormous robots that transform into vehicles. They are taken to the base of the Autobots, where their leader Optimus Prime explains that he and his team (consisting of Ratchet, Bulkhead, Arcee, and Bumblebee) are autonomous alien robots from the planet Cybertron. The Autobots once had a devastating war against the tyrannical Megatron and his army, the Decepticons, and the war made Cybertron uninhabitable. Megatron returns from a three-year-long exile in deep space with a sample of Dark Energon, which can revive dead Transformers as mindless zombies called "Terrorcons", and he sets out to conquer Earth with a Terrorcon army brought over from Cybertron through a Space Bridge. The Autobots foil his plan by destroying the Decepticon's Space Bridge, and as Megatron is caught in the explosion he is presumed dead.