Dark Horizons ( novel ) Dark Horizons was the third long - length Eleventh Doctor novel . Publisher ' s summary . " " Now , you may or may not have noticed , but we appear to be on fire . . . " " On a windswept Northern shore , at the very tip of what will one day become Scotland , the islanders believe the worst they have to fear is a Viking attack . Then the burning comes . They cannot run from it . Water will not stop it . It consumes everything in its path — yet the burned still speak . The Doctor is just looking for a game on the famous Lewis chess set . Instead he encounters a people under attack from a power they cannot possibly understand . They have no weapons , no strategy and no protection against a fire sent to engulf them all . Add in some marauding Vikings with very bad timing , a kidnapped princess with a secret of her own and a TARDIS that seems to have developed an inexplicable fear of water , and they all have a battle on their hands . The islanders must take on a ruthless alien force in a world without technology ; without communications ; without tea that isn ' t made out of bark . Still at least they have the Doctor on their side . . . Don ' t they ? Plot . Just off the coast of the land that will one day become Scotland , a Viking ship transporting Freydis of Trondheim to marry Gissar Polvaderson is set alight by some creature that seems to burn on the surface of the water . The Eleventh Doctor arrives and swims towards the ship to rescue the survivors . Upon returning to shore , the Doctor convinces Corc , the chieftain of the village Lowith , to help the Vikings . Despite an aggressive protest from his oldest son Eoric , Corc agrees and the villagers and Vikings spend the night together . During their stay at the village , Freydis befriends one of the Vikings named Henrik who agrees to be her guardian . Freydis also believes the Doctor is a God , Loki , who has plans for her . Eoric becomes bitter at his father and younger brother Luag for helping the Vikings . He expects them to attack the village soon and sulks , thinking about the death of his mother at Luag ' s birth . Some time later , as the Doctor attempts top call the creature out at sea to communicate with it , Eoric hears a whisper . Soon , another Viking ship appears off the shore . The Doctor and Henrik rescue them before their ship can be set on fire and bring them back to shore . These Vikings were sent to follow Henrik ' s ship and ensure they delivered Freydis to Gissar instead of deserting with their valuable cargo . The leader , Erik , gives the order for his men to begin pillaging but Eoric , under the control of another entity , appears with mysterious and dangerous fire abilities and chants about continuing “ the line ” . The creature inside Eoric begins attacking the Vikings but Luag approaches it and asks for his brother back . The Doctor grabs Luag before he is killed but Eoric explodes and burns up , leaving nothing but a charred corpse . Some of Erik ' s Vikings use this event as a distraction and they capture Freydis again , taking her away on their ship . The Doctor collects Henrik for help and they leave in the TARDIS to pursue Erik and Freydis . On the ship , Freydis manages to escape the interior using a piece of scrap metal which she makes into a weapon . She threatens to slit Erik ' s throat in front of his men if they refuse to return her to the village . Just then , the TARDIS appears but it proves too heavy for the ship ' s flooring and breaks through , Freydis and Erik jumping after it and getting inside just in time . The TARDIS finally ends up at the bottom of the sea as the Doctor , for some reason , has trouble convincing her to dematerialise . The Cloister Bell sounds . Putting on an old diving suit , the Doctor leaves to investigate the seabed after teaching Henrik and Freydis to pump the air into the suit . Despite the TARDIS air pocket , some water begins leaking in from the roof . Outside , the Doctor finds the Consciousness of Arill , an entity which feeds off electricity and was attracted to Earth by the electrical signals in human brains . Eoric was possessed to see if it was possible for the Arill to feed of this electricity . It is also the reason the TARDIS would not dematerialise , as the Arill could have fed off its power if it detected it . The Arill were unable to make contact with humans because it began burning after leaving the water . . Back in the TARDIS , Erik begins working at the controls to get the ship to leave . Henrik and Freydis fight him but not before the TARDIS begins to dematerialise – causing the doors to snap shut and the Doctor ' s air pipe to be cut . The TARDIS materialises again in the same place but the Doctor is trapped out on the ocean floor after the Arill leaves him . His extra lung capacity once noted to him by Martha Jones helps to keep him alive for longer than a human but not forever . Henrik finds the Doctor ' s space suit from Sanctuary Base 6 and uses it to bring the Doctor back to the TARDIS before he drowns . Back inside , the Doctor explains to them that the Arill are exploring space in search of electricity to feed on . Back at the village , Eoric is given a funeral . No feast is held afterwards as the village is running low on food suplies . Afterwards , Henrik and Freydis share a kill while the Doctor comforts Luag by playing games with him despite the threat of a storm . Luag is then called for by his carer Brogan , who has taken over by the Arill like Eoric . Braan , Brogan ' s partner , kills her to end her suffering . A meeting is held concerning how the Arill should be dealt with . It is agreed that no fire ' s shall be started so the Arill cannot travel through them . Freydis becomes angry at the Doctor for not taking any action even though he is very powerful . The Doctor begins to formulate a plan to use the oncoming storm to allow the Arill to leave . Later , the Doctor is teaching Luag how to play chess when Erik and his Vikings threaten once again to attack the village . Erik attempts to bargain with the villagers , saying that they will leave in peace if they are given Freydis , materials to repair their ship and some food . The Doctor , displaying his skills with a sword to Erik , prevents a fight and it is agreed that both sides will help find food before anyone can leave . However , one Viking drops a torch which slowly begins to set the grass on fire . At the beach , the Doctor sends a message via Psychic paper to the Arill , giving them one more chance to stop killing people . The Arill respond by dispersing and appearing to surface from the water and burn up in an act of sacrifice to let the villagers live . Elsewhere , two of Erik ' s Vikings , Lars and Olaf light a fire despite the warnings they were given . The Arill , having faked their death , possess them and they begin setting fire to the village . The villagers rush to extinguish the flames . Erik and some other Vikings willingly embrace the Arill to become powerful . Corc too becomes hopeless , almost hysterical , and runs towards them but he is knocked back by Henrik . Henrik himself gets to close and is possessed too . Freydis wraps her hands in some clothes and pushed him back to the ocean where she holds him under . He is lifeless when Freydis surfaces him . The Vikings taken by the Arill burn up . The Doctor is furious at the Arill for tricking him , even after he gave them a chance and offered them his help . He collects the village ' s swords from Corc and begins constructing a lightning rod as Luag tells the Doctor his ears are popping , meaning a storm is approaching . The Doctor takes a coracle out to sea and begins speaking with the Arill again . He informs them that he still intends to help them and allows the Arill to feed on him . As they take him over , the storm arrives and the Doctor holds up the spear of swords . Lightning strikes it and the Arill are sent into the atmosphere . The Doctor collapses and the villagers watching from the coast presume him dead . The Doctor wakes up in the coracle later . He still feels warm even though the weather is cold , some essence of the Arill remaining within him . When he returns to land , he has the remaining essence take on the form on Eoric and Brogan for a brief moment , allowing Corc , Luag and Braan to say a proper goodbye to their loved ones . The Doctor stays at the village for a while longer , playing more chess with Luag and answering any final questions the villagers have . He gives Henrik , Freydis and the remaining Vikings help for when it comes to navigating their way back home once they repair the damage the TARDIS did to Erik ' s ship . Before leaving , he gives Henrik and Freydis an offer to travel with him but they turn it down . The Doctor says the last of his farewells before pressing down the accelerator and taking off .