Roots: There are references to the Isley Brothers, Desperate Housewives, Star Wars, Frankenstein, Meccano, Cher, and Journey’s “Don’t Stop Believing”.
Continuity: The androids are designed as assassins and special forces, able to infiltrate enemy territory without putting the lives of US soldiers at risk. They are virtually indestructible, although they can be stopped with a focused sonic pulse or a nuclear explosion.
The sonic screwdriver has a Geiger setting. The Doctor has a gold-plated watch. He uses the psychic paper to convince a sergeant that he has an American Health and Safety Pass – Access All Areas, and later poses as a Pentagon official. He carries string and scissors.
Rory and Amy got food poisoning from some frozen pies in September. Rory gets scratches on his arm in Appletown and later burns his hand.
The TARDIS console room still contains a hat stand.
Location: Chicago Illinois, 23rd February 1973; University of Michigan, 23rd to 24th February 1973; Colorado, 28th August 1981; California International Conference Centre, 3rd August 1975; Utah Military Research Base, 27th May 1977; Florida Airbase, 3rd February 1980; and Washington DC, 28th February 1981.
The Bottom Line: A nice conceit, but the logic doesn’t quite work, causing the story to creak somewhat. The actually plot is quite slight, forcing Smith to sideline Amy and Rory - who spend the entire story evading robots.