Doctor Who-The Visitation

                         Attempting to return Tegan to her original location of Heathrow airport shortly after she was set to arrive,the TARDIS finds itself in mid 17th century England in the same location to find the smell of gunpowder smoke in the air. They are soon set upon by a man addressing himself as a Richard Mace-an actor turned highwayman following an enormous display of shooting stars preceded a plague in the area that has killed hundreds. When Nyssa locates alien power packs in the vicinity,the doctor and his companions,Mace included journey to the nearby home of the Miller where Mace intends to intact his latest heist. When inside the Millers after his departure,they all find his home deserted-along with the smell of Soliton gas around him-something that clearly does not belong in 1666. 

                    Following with his sonic screwdriver to its source he locates a holographically hidden door,behind which is located alien a caged rates and a winery. The doctor and his companions are set upon by an android disguised as the Grim Reaper,who while frightening Mace and capturing Tegan and Adric help the doctor and Nyssa to realize for sure that the shooting stars seen before the beginning of the plague are surely extra terrestrial in origin. The doctor recognizes the android as belonging to a species known as the Terireptiles. Of course the green skinned amphibian like Terireptile's,at least one of them is demanding Tegan and Adric give him information on the TARDIS and the doctors sonic device. 

               While Tegan is taken away the doctor,Nyssa and Mace travel to what turns out to be a Terireptile escape pod. Adric is let go and is sent by the doctor with Nyssa back to the TARDIS to build a sonic disrupting device to counter the effects of the Terripetiles android lackey. After pointing out to Mace that the pendant he found is actually a Terireptile mind control bracelet,the doctor and Mace attempt to speak to the Miller,who doesn't acknowledge them but the mind controlled villagers soon set upon the doctor and Mace. They are rescued by the Miller who takes them alive to the Terireptile who,as it turns out is not only controlling Tegan with the same bracelet used to control the villagers but is one of four Terereptile prisoners who escaped mistreatment when their ship crashed on Earth.

              Unable to travel to another world,the doctor offers the Terireptile a chance to either return home or to an uninhabited world with him. The Terireptile,an intelligent but imperial race,intend to unleash a systematically lethal plague to destroy all human life so they can colonize the Earth.  Upon resisting,the doctor and Mace are imprisoned. While Mace is controlled by the bracelet same as Tegan,the doctor attempts to engineer an escape-after which the Terireptile destroys his sonic screwdriver. While Adric attempts to set off on his own from Nyssa to fight off the controlled villagers,Nyssa is successful at building and setting off the sonic device and destroying the android. Once back inside the TARDIS with an amazed Richard mace,the doctor localizes the Terireptile base in London. 

               Arriving to the Terireptile feigning surrender inside a bakery where Miller is delivering the devices intended to distribute the plague into the many rats in London,the bakery is accidentally set on fire to the bakery. Unable to save the itinerant Terireptiles as intended,the doctor and his companions are able to make an escape. Richard Mace is invited by the doctor to join him in the TARDIS,but declines due to the fast paced nature of what he's experienced and elects to stay behind to help put out the fire. While Nyssa ponders the logic behind the doctor leaving a Terireptile device with Mace as a memento he reveals to her,Tegan and Adric that the  burning bakery they just escaped was the Thomas Ferriner's Bakery on Pudding Lane. And they had inadvertently started the Great Fire Of London.

               Throughout this story,time and history are the most important points. The doctor's presence in 17th century England is just as interwoven into the fabric of human history as the Terireptiles: with the former causing the Great Fire Of London and the latter causing the great plague. Only Richard Mace,a companion who only followed the doctor due to his own opportunism and cowardice in the beginning,was aware of the significance of these events. Aware that the locals around them view the extra terrestrial events in only a supernatural context,the Terireptiles are thoroughly unimpressed by the doctors urgent pleas not to destroy humanity for their own benefit. 

                 Of course history is made here for Doctor Who itself,as the sonic screwdriver is destroyed-never appearing again for the rest of the classic series run on BBC due to writers feeling it was too easy a plot device. Overall a wonderful serial in which each companion in the "crowded TARDIS" got their own vital function in assisting the doctor-in particular the often underused Nyssa. Michael Robbin's terrific blend of dramatic hubris and superstition in his characterization of Richard Mace made him a companion,while I personally wish had been a different case,whom we'd never see again in Doctor Who on TV. A fine addition to Doctor Who's consistent 19th series.