Original: They emerged, along with a Time Lord prison vessel containing millions of Daleks, at Canary Wharf due to the actions of the Torchwood Institute and Cybermen from a parallel world.
Simplified: They emerged, along with a Time Lord prison containing millions of Daleks, at Canary Wharf due to the actions of the Torchwood Institute and Cybermen from a parallel world, leading to a Cyberman-Dalek clash in London.