Flip - Flop ( audio story ) The play was further notable for being the closest the Quark s have ever come to returning to performed " Doctor Who " since " The War Games " . Though never heard , the Quarks are essentially the of the story and are mentioned at least once in each episode . From the Doctor and Mel ' s perspective , the events of " Flip - Flop " were merely a side - trip from their current " mission " to defeat the Quarks aboard the space yacht " Pinto " . Publisher ' s summary . Christmas Eve in the year 3060 and the planet Puxatornee is home to a prosperous human colony . A space craft has arrived in orbit carrying the Slithergees , a race of obsequious alien slugs . Their home world has been destroyed and they are humbly requesting permission to settle on the first moon . And if they don ' t get permission , then they are humbly threatening to declare all - out war . The future hangs in the balance . The decision rests with Bailey , the colony ' s president — but she has other things on her mind . . . Christmas Eve in the year 3090 , and the planet Puxatornee has changed beyond all recognition . The Doctor and Mel arrive , on a completely unrelated mission to defeat a race of terrible monsters , and soon discover that something rather confusing has been happening to history . . . Plot . Part one ( white Disc ) . The Doctor and Mel land on Puxatornee on Christmas Eve , 3090 , in search of Leptonite crystal s . The Doctor is disturbed to find the war - ravaged colony on its last legs . Security agents Stewart and Reed promptly arrest them as self - confessed Slithergee spies . To their surprise , they are soon rescued from jail by an entirely " different " Stewart and Reed who are killed before the Doctor and Mel can ask what ' s going on and why everyone seems to know them . Confusion ensues , with paranoid President Mitchell ordering his security forces from one side of the city to the other chasing conflicting reports of the escapees ' whereabouts . Meanwhile , Mel and the Doctor discover the laboratory of Professor Capra , inventor of a one - way time machine . The Doctor vows to stop the humans from meddling with their own history . Mitchell plans to send Lieutenant Stewart and Lieutenant Reed back in time to save President Bailey , whose assassination 30 years ago led to war with the Slithergees . The humans won that war , but at great cost . Radiation , poisoned fields and martial law have made life on Puxatornee unbearable . Mel and Stewart are flung back to 3060 by Capra ' s machine , which then overloads and destroys Puxatornee in 3090 . The Doctor and Reed escape in the TARDIS before that happens , but are too late to stop Stewart from killing Clarence , Bailey ' s supposed assassin . The Doctor can ' t bring himself to kill President Bailey to restore history . Reed and Stewart tell President Bailey that they came from a terrible future where war ruined Puxatornee , and they insist she make peace with the Slithergees at any cost . Part two ( White Disc ) . The Doctor takes Stewart and Reed forward to Christmas Day 3090 in the TARDIS , but history has now changed . President Bailey , the " Great Appeaser , " has capitulated to all the Slithergees ' demands , allowing them to occupy not only Puxatornee ' s moon but eventually the planet . Humans have become slaves , and their culture is being erased even as the Slithergees demand retribution for " hate crimes " and discrimination . Officers Stewart and Reed are horrified . This is not the future they wanted . They demand the Doctor take them back to the previous night , Christmas Eve 3090 , to stop themselves just before they embarked on their mission to save Bailey . He complies , but he can ' t return them to the timeline they ' ve erased . Stewart and Reed are killed by Potter , an officer who served under them in their own history , but who is working for the Slithergees in this one . The Doctor and Mel , meanwhile , re - encounter the alternate Stewart and Reed , rebels against Slithergee occupation . The rebels don ' t recognise them , but learn from a careless comment of Mel ' s that the Doctor has a time machine . The Doctor and Mel realise that not only are there alternate versions of Potter , Stewart and Reed running around , but that their own counterparts will shortly materialise in the same place where they landed . Having secured the Leptonite crystals they need , they rush back to their TARDIS and dematerialise in the nick of time , trusting that the alternate Mel and Doctor will sort out Puxatornee . Part three ( Black Disc ) . The alternate Doctor and Mel land on Puxatornee on Christmas Eve , 3090 , in search of Leptonite Crystals . Mel is disturbed to find humans enslaved to the Slithergees . Potter and his Slithergee master promptly arrest them as dissidents . He takes them to Professor Capra for interrogation . Two rebels , Stewart and Reed , burst in and free them . To Mel and the Doctor ' s surprise , the strangers seem to know who they are . They want to use the Doctor ' s time machine to go back in time and kill Bailey before she gives in to the Slithergees ' demands . Bailey , meanwhile , has lost faith in her deputy , Mitchell , whom she suspects has been serving the Slithergees all along . She believes he staged the assassination attempt 30 years ago and hired two imposters to dissuade her from war . The quarrel ends with Bailey dead . Suicide , Mitchell tells the Slithergee Community Leader , although she apparently tried to shoot him . The Community Leader hails Mitchell as the new president , but soon kills him , making Puxatornee the " Planet of the Slithergees " . After Stewart threatens to shoot Mel , the Doctor has no choice but to take him and his associate back to 3060 . Stewart and Reed kill Bailey ' s secretary , Clarence , then execute President Bailey for crimes she has yet to commit . Stewart leaves the gun with Clarence to make it look like a murder - suicide . Part four ( Black Disc ) . The Doctor takes Stewart and Reed forward to Christmas Day 3090 , but history has now changed . Choosing to believe Clarence was a Slithergee agent , Mitchell declared war on the Slithergees in retribution . The war left Puxatornee a toxic wasteland , with starving humans eking out a miserable existence under martial law . Mel and the Doctor are arrested as " enemy agents " by officer Potter . He is tricked into handing over his prisoners to the rebel Stewart and Reed , who pretend to be Potter ' s superiors , Lieutenant Stewart and Reed . The dissidents are horrified . This is not the future they wanted . They demand the Doctor take them back to the previous night , Christmas Eve 3090 , so as to stop themselves before they embark on their quest to kill Bailey . The Doctor drops them off on the previous night as requested , but it ' s the new , postwar timeline . The rebels wander off and become lost . The Doctor and Mel , meanwhile , run into all the security agents again — for the first time , from the POV of Officers Potter , Stewart and Reed . In order to preserve history , the Doctor and Mel confess that they are Slithergee spies , since they know Potter will arrest them as such tomorrow morning . Mel points out that there must be another Doctor and Mel in this timeline , and the Doctor realises they need to dematerialise before their counterparts arrive . Having secured the Leptonite crystals they need , they rush back to their TARDIS and leave , trusting that the alternate Mel and Doctor will sort out Puxatornee .