Set in 2068, the series depicts a "war of nerves" between Earth and the Mysterons: a race of Martians with the power to create functioning copies of destroyed people or objects and use them to carry out acts of aggression against humanity.
Earth is defended by a military organisation called Spectrum, whose top agent, Captain Scarlet, was killed by the Mysterons and replaced by a reconstruction that subsequently broke free of their control.
As with the episodes "Winged Assassin" and "Big Ben Strikes Again", similarities between the plot and the September 11 attacks caused "The Heart of New York" to be postponed for several weeks during BBC Two's 2001–2002 repeats of the series.
When the lookout's story reaches Cloudbase, Colonel White decides that he will not risk lives to protect the bank and orders all Spectrum personnel to retreat to the roadblocks.
Learning of the men's arrival, Scarlet is puzzled how a group of supposed government agents knew that the Mysterons were specifically targeting the bank when only Spectrum personnel had been informed.
Back on Cloudbase, White concedes that Kruger, Doig and Carl exemplified the greed and corruption denounced by the Mysterons, but insists that the good of humanity will eventually prevail over the Martian evil.
[6] The Carl puppet previously appeared as Lieutenant Belmont in "White As Snow" while the fire lookout also played Major Brooks in "Point 783" and Air Commodore Goddard in "The Trap".
[7][8] James Stansfield of Den of Geek considers "The Heart of New York" the second-best episode of Captain Scarlet, regarding it as "memorable and unique" because "the Mysterons [are not] really the villains".
He believes that the episode fundamentally serves as a "character study on the consequences of greed", arguing that its "grey depiction of morality" was unusual for a TV series that was written primarily for children.