The Enochai were a race of pure energy who attempted to take over the Earth in 2009.
Their ship was buried underground, and they were trapped there, stuck in their clockwork bodies. The Enochai had previously tried to manipulate John Dee, but he stopped them, destroying some of their physical bodies and trapping one of them in cryogenic suspension. The Enochai who had lost their bodies possessed the trees in Greenwich.
The Tenth Doctor was lured into a trap and unknowingly freed the Enochai from cryogenic suspension. The rest of the Enochai were then freed, and attacked Greenwich and Central London.