"Avalanche" is the 11th episode of Captain Scarlet and the Mysterons, a British Supermarionation television series created by Gerry and Sylvia Anderson and produced by their company Century 21 Productions.
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.
Obtaining a Spectrum Pursuit Vehicle from a trapper, Scarlet and Green speed to the next base, Big Bear, only to learn that Eddie has already passed through and is now on his way to the Frost Line command centre.
Actor Shane Rimmer had a prior association with Century 21, having voiced the character Scott Tracy in Thunderbirds and narrated the series' alternative two-part episode format.
[11] Fred McNamara writes that the episode successfully "balances adventure and atmosphere" with an "evolving sense of dread", adding that its "familiar premise, sublime model and set work, excellent pacing, and overarching themes of power and war" make it a "highly rewarding" instalment.
"[14] McNamara applauds the casting of dual adversaries, Mysteron and military, writing that the latter's "trigger-happy stubbornness" in the face of alien aggression blurs the boundary between heroes and villains and reveals a grey morality.
He considers the ending all the more effective for the absence of a "clean resolution" between Spectrum and its Earth-bound opponents, noting that there has been no "epiphany" for Ward's forces and the general himself is no less arrogant than he was at the beginning of the episode.
[14] Stansfield, who considers the demise of the original Eddie particularly violent, calls the death toll "easily ... the highest body count of the series" and "a pretty large number for any TV show, let alone one for youngsters".
[11] "Avalanche" is one of only a few episodes in which Lieutenant Green plays a significant role, joining Scarlet in the field while Captain Blue steps in as communications officer aboard Cloudbase.