250px-Reptilian Alien

The Skerth were a species of alien with misshapen rat skulls from an unknown planet that had crash landed on the pirate ship fancy in an alternate dimension. The crew all caught a disease from earth (quite possibly a cold) and perished as they had no imunity to it. A virtual medic (the siren) was activated but it had no patients to help so it went to the pirates dimension instead. The Skerth's ship was dscovered by the Doctor, Amy and Captain Avery, and the ship was taken by Avery and his crew.