The Instruments of War ( comic story ) Plot . Part 1 . In the desert , several camel riders watch a plane crashing using advanced binoculars . One orders the others to activate " the device " . In the TARDIS , Clara is eagerly awaiting her arrival at the Frost Fair of 1641 , having decided to go and see for herself because some of her students are doing a project on the subject . The Doctor is a bit grumpy about going at Christmas , considering how long he lived in the town , as well as some odd readings on the TARDIS console , and isn ' t cheered up by Clara referring to his being carried around in her handbag a week earlier . Unfortunately , the TARDIS arrives in sand , not snow , with no buildings in sight — it ' s the Sahara Desert . While looking for someone to ask directions from Clara spots a tank , which the Doctor identifies as a Matilda model , used by Allied forces during World War Two - it seems they ' re in 1941 , not 1641 . The tank , unfortunately , turns out to be a German tank , which takes them prisoner . In German Headquarters , Field Marshal Rommel is arguing with Oberst Bruckner about orders to use saturation bombing against the Allies , despite his troops having settled into winter quarters with established supply routes . They are interrupted by " Doctor Johan Schmidt and his assistant Fraulein Oswald " from Berlin , but Rommel is able to see through the psychic paper that got them to him . It turns out that the Germans ' Tuareg allies have reported " new friends from the sky " , making the Doctor realise that the TARDIS brought them here for a reason . He arranges to go with Rommel to meet the Tuareg , whilst Clara stays behind to snoop around . She quickly strikes up a friendship with the young Unteroffizier Hans Engel , who turns out to have been a cellist in civilian life , but they are interrupted by an equally nosy Bruckner , unconvinced of " Fraulein Oswald ' s " credentials . The Doctor and Rommel head to the rendezvous , with the Time Lord sadly remembers all the wars he ' s been involved in , and that he always tries to find another way out where everyone lives . When Rommel says that how they comport themselves at death is the measure of a man , the Doctor refers obliquely to the Field Marshal ' s own death in 1944 . When they do find the Tuareg , they are using energy weapons ; the Doctor promptly uses his sonic screwdriver to cause a light - show that impresses the tribesmen rather than hurts them and demands to be taken to their chieftain . Back at German HQ , Bruckner orders Engel to prepare a rescue party to " save " Rommel from the Doctor , but also quietly tells Clara that he knows she ' s not a spy despite her 1641 gown " because I am " . . . At the Tuareg camp , their chieftain , Bhaki , welcomes the Doctor and Rommel and happily agrees to introduce them to the men from the stars . The Doctor becomes visibly concerned after recognising the weapon in the tent , proclaiming " This is bad , this is very " very " bad . . . " , and with good reason : the visitors are Sontarans , led by Kygon Brox of the Eighth Sontaran Battle Fleet . Part 2 . Bruckner orders Engel to bring " Fraulein " to the grief ; Engel fails to believe that Clara is innocent . That said , Engel and Clara are heading towards the Doctor , giving Clara some hope . Back at the Tuareg camp , the Doctor urges Rommel and the Sontarans not to fight ; after all , they have a good amount in common , and there is little cause for battle . Brox , however , is interested in something else - the Doctor . Recognising the time traveller as nonhuman , Brox assumes the Doctor to be an enemy searching for the Warsong . Clara admits to Engel that she is not German , but also maintains that she isn ' t a spy . After she explains Bruckner ' s unfaithful intentions , Engel concludes that Clara cannot be a spy after all — a spy would not say such a ridiculous , implausible thing . The Sontarans , still convinced that the Doctor is in search of the Warsong , order him to say what he knows , eventually using a mind scythe to get the information out . Bhaki , having seen men " reduced to a husk " with the device , concludes that the Doctor is beyond help . . . Engel notices that Bruckner is not going in the direction of the Tuareg encampment . Bruckner orders his driver to halt at this point ; he and his soldiers unload their crates of wooden planks , building a structure . Back with the Sontarans , the Doctor is showing Brox " holiday snaps " of past adventures , before explaining that the mind scythe can in fact go both ways . He proceeds to probe the mind of a shocked Brox . While Engel is incredulous of Clara ' s claim to be a time traveller , Bruckner sees the notion as perfectly plausible ; in fact , her revelation has resolved a conflict he had been working on for a good amount of time . He then confesses that he is indeed a spy — but not a British one . . . Using the mind scythe , the Doctor discovers that the Warsong Brox was referring to is a " world engine " that changes the course of war . Despite creating the weapon , the Sontarans struggled to deploy it , so they took it to a primitive world . The weapon lay dormant on Earth for years , only activating when it sensed aggressive technology ; however , once Earth reached a level of technological advancement that could be viewed as threatening , the Warsong began to awaken . Hearing the weapon ' s " overture " , Brox ' s battle fleet came to Earth ; however , its signal is not yet strong enough to be fully utilised , so the Sontarans can currently do nothing but try to stop the enemy that seeks it . After convincing Brox that both himself and Rommel can be useful to the Sontarans ' goal , the Doctor uses his sonic screwdriver to destroy the mind probe . Meanwhile , Engel attempts to relieve Bruckner from his command ; however , after acknowledging Engel ' s less - than - satisfactory life , the spy shoots Engel with bolts of green energy . Back at the Tuareg camp , the Doctor and Rommel discuss Bruckner ' s recent behaviour . The Doctor suggests that his depletion of forces and resources may mean he is wishing to do something more than win the war — more specifically , something involving the Warsong . What ' s more , the Doctor believes that Bruckner may not be who — or what — everyone thinks he is . . . Bruckner uses the Warsong to kill all of his soldiers who are at the location . He explains that the TARDIS ' energy is what powered the weapon enough to do so , and that she has helped him satisfy his people : the Rutans . From a distance , the Doctor and the Sontarans see the Warsong ' s energy . Brox explains that the weapon ' s description of " world engine " is quite literal : it will take the energy from people , buildings , and natural formations to turn the entire planet into a weapon . . . Part 3 . Seeing that Bruckner has Clara , the Doctor decides to save her , despite the extreme danger . Brox initially dismisses his action as reckless , but the Doctor insists that he is in fact thinking hard : they could pool their resources and seize the not - yet - fully - formed Warsong , for the glory of Sontar . Rommel protests , but the Doctor insists that being on the winning side would be preferable to defeat , regardless of innocent lives taken . However , while out of Brox ' s hearing range , the Doctor explains that he was merely telling the Sontaran what he wanted to hear . Bruckner teaches Clara of the Warsong , explaining that the dead soldiers as well as the surrounding sand were used to power it , with the rest of the planet to soon follow . The Doctor , meanwhile , suggests that the machine may be vulnerable whilst it is still growing . Launching as much as they can at it , at as great a speed as possible , might result in " a lucky break " in the weapon ' s defences - seemingly their only hope for victory . The Doctor phones Winston Churchill , ensuring that the Allies attack from the other side at the same time as the Axis . Initially , the Warsong simply destroys the attacking vehicles with ease . However , using his sonic screwdriver , the Doctor changes the harmonic resonances of a tank . As the Warsong ' s technology is based on sound , the tank is now able to attack the weapon , as well as enter it . Bruckner suggests that Rommel join him , but the German refuses to take part in the destruction of every human being on Earth . Whilst the Doctor distracts Bruckner , Brox manages to enter the Warsong as well , giving the Time Lord an osmic projector . Bruckner grabs Clara and holds her at gunpoint to stop the Doctor from sending him back in time ; however , instead of sending him back in time , the Doctor uses the projector on his gun . Rommel proceeds to push Bruckner off the safe platform they are standing on , into the energy conversion part of the Warsong . Brox announces the weapon as Sontaran property , but the Doctor reveals his true intentions . However , the Sontaran is severely weakened at this point , and he perishes before he can do anything to the Doctor . The Doctor uses his sonic screwdriver once again , this time destroying the sound - based Warsong . As everyone escapes , the machine explodes . The Doctor notes the irony of the culturally - bereft Sontarans creating something as lyrical as the Warsong . He suggests that this artistic side of their nature has been bred out , explaining their inability to recreate the weapon . He also assures Rommel that this entire event will be forgotten by the collective of humanity , which will focus instead on finishing World War II . After this conversation , the Doctor and Clara finally make it to the Frost Fair of 1641 . They discuss Rommel , who eventually joined the Valkyrie conspiracy to remove Hitler from rule . After this was discovered , he was given two options : either he would commit suicide and his family would survive , or he would stay alive and his family would be killed . As he chose the former option , this man of war ended up dying for love ; and , as the Doctor states , " There are worse things to die for . " External links . " to be added "