Deathy was an alien.
He worked as a bounty hunter with red skin and three eyes. He hacked himself into Mr Smith and was using him for his own purpose. He wanted to lock Skak in time while he caught another criminal. Mr Smith hadn't realised it because he had still been suffering from the computer viruses. (AUDIO: The Ghost House) The computer virus was uploaded by Alan Jackson to stop Mr Smith from destroying the earth to set the Xylok free. (TV: The Lost Boy)
Skak contacted another crimal Ephnol, and Ephnol tried to set Skak free which caused the house of the O'Brians and a Victorian house to swap places in time. Deathy caught Skak together with Sarah Jane Smith and her team and put the houses into the right time again. He also made sure that the Burden family forgot about the swapping of the houses. (AUDIO: The Ghost House)