The Secret Heart was one of the last Racnoss spacecraft after the war between the Racnoss and the Fledgling Empires. It was similar in design to the Empress of the Racnoss' ship, the Webstar, and was also powered by Huon particles.
Roughly 4.6 billion years BC, the Secret Heart escaped the war with a complement of hibernating Racnoss young. It entered the Sol system and drew rocks and dust around itself for camouflage, becoming the nucleus of what would become the Earth.
The Torchwood Institute discovered the Secret Heart at the Earth's centre and secretly drilled a borehole to it under the Thames Flood Barrier. After the Battle of Canary Wharf, the operation was taken over by the Empress of the Racnoss. On 24 December 2007, she used Huon particles to awaken her "children" on the Secret Heart.
The emerging Racnoss were drowned when the Tenth Doctor blew a hole in the Flood Barrier, allowing the River Thames to drain into the borehole. (TV: The Runaway Bride)
