Doctor Who-The Android Invasion

                Upon arriving back on Earth to UNIT HQ the doctor and Sarah-Jane Smith find an unusually high radiation count and,soon enough,menaced by unusual suited guards and a UNIT soldier who threw himself over a cliff. The pair soon land in the town of Devesham, where Sarah once did a news report in her days as a journalist and where the local population are acting very suspicious. After moving onto UNIT HQ they find the facility has been taken over by Guy Crawford,an astronaut Sarah understands to have been dead. After fleeing UNIT HQ after being attacked  the doctor is confronted with the horrible truth:  this is not Earth,the people they encountered were actually pre-programmed androids and,while escaping the false UNIT HQ the person he believes was Sarah was actually an android as well. During this process,the real Sarah accidentally diverts the TARDIS to the actual Earth par it's fail safe mechanism. When Sarah and the doctor are taken by Crawford and the androids to an alien vessel both of them learn the true motivation behind all this. 

             A planet called Kraal has become dangerously radioactive. And this race,lead by surgeon Styggran,are planning to invade Earth with a group of androids carrying  a deadly virus that will destroy humanity and leave the planet open to Krall colonization. Upon using their mind/body replication device to replicate the doctor,Sarah and the genuine doctor escape back to Earth on the Kraal rocket intended to deliver to deadly androids. Meanwhile confusion runs so amok at the real UNIT HQ at the empty TARDIS's appearance they are not aware of the true intentions of Crawford's return. Not to mention that Harry Sullivan and Benton have already been replaced by androids-as well as the doctor himself,and are already laying the groundwork for the proposed invasion. Upon successfully averting the invasion,the real doctor also stops a coup by the Androids  when Crawford switches sides and is killed by Styggran,the doctor and Sarah return to their journey in the TARDIS.

             As a whole this story is fully representative of all of the best qualities of Doctor Who during the mid 1970's. The chemistry between Tom Baker's fourth doctor and Elizabeth Sladen's Sarah-Jane Smith serves as the main strength motivating this entire adventure. And it's also a very compelling story at that. It mashes up both The Andromeda Strain  and Invasion Of The Body Snatchers in order to comment on the pretentiousness of Earth defense forces to successfully stop an intricately planned extra terrestrial invasion. With it's very clever use of what minute special effects Doctor Who was given at the time in terms of available budget,this story managed to visually convey the sense of uncertainty and deception it was looking to convey. And again as was typical for the era,the fact that the doctor was in a type of danger that genuinely effect his life and that of his beloved Earth added to the strengths of this story as well.