Hervoken The Hervoken were an ancient species . Biology . The Hervoken were approximately ten feet tall , with an extremely thin body but a colossal head that somewhat resembled a Halloween jack - o ' - lantern . Their hands were about as long from the wrist to the fingertips as a human arm , and their fingers had several joints and a talon at the end . Their heads were pale and fleshy , with sharp teeth and black , beady eyes . Hervoken had high - pitched , almost childish voices . Hervoken laughter was made up of clacking their teeth together to produce green sparks . ( PROSE : " Forever Autumn " ) Culture . Hervoken were insular by nature , and tried not to deal with others if they could . They had little of the curiosity that human s had and were content to simply keep to themselves . Because of this , they seemed remarkably callous in their nature . The Hervoken language was complex , and consisted of words , body language , thoughts , incantation and pauses . As such , simple acts like chanting or resting or praying were actually methods of communication . ( PROSE : " Forever Autumn " ) Technology . Their technology was very much like magic in appearance and effect . It was activated by drawing sigils in the air or chanting . It would be weakened by the use of salt and iron . Hervoken relied on agents , which were created by animating inanimate matter and modifying existing beings . These agents would be able to do new things , but they would not change in basic structure ( a plastic bat may be able to fly and attack , but it would still be plastic ) . Hervoken ships were known as sky - heart s . ( PROSE : " Forever Autumn " ) History . The Hervoken were an ancient species , though they kept to themselves for most of the time . At some point , millions of years ago , they got into a war with the Carrionite s . The details of this war were vague , but it was implied to have been very destructive , as the Eternal s were forced to step in and banish both races to the Deep Darkness before the universe was destroyed . One Hervoken ship escaped , since it was on Earth at the time and escaped the notice of the Eternals . The ship lay dormant for many years , attracted people to area to maintain it . They soon passed into the myths of the Niantic s , being known as the " Hee - oko " . Eventually , the town of Blackwood Falls was built on top of the Hervoken ship . The Hervoken were able to psychic ally influence the inhabitants , making them create cellars into the Hervoken ship so they could be used for fuel . The side - effect of this was that Etta Helligan ' s family developed psychic powers . Eventually , the ship repaired itself completely . When the Hervoken were reawakened in the early 21st century , they planned to repower their ship with energy from the town ' s inhabitants during the upcoming Halloween celebration . The launch of the ship would have devastated the town and most of the surrounding area , but the Hervoken were defeated by the Tenth Doctor and Martha Jones . ( PROSE : " Forever Autumn " ) Mentions . When Vida Clatterly expressed the belief that magic was not real , the Eleventh Doctor told her about about the Hervoken , among others , who used science disguised as magic and explained that belief is a very powerful thing . ( PROSE : " The Dreaming " )