The AB Chrysalis

Background

In the episode, the Moon is hit by increasingly powerful shockwaves originating from a nearby planet. Commander Koenig, Maya, and Captain Carter investigate and find a moon with balloon-shaped buildings and a cavern of spheres on stands. Koenig realizes the spheres are sentient machines that communicate via charts; they explain that only their organic "Masters" can shut down the planet's defenses. The Masters are in chrysalises, awaiting rejuvenation.

The Alphans land on the planet and meet Voice Probe 748, which explains the rejuvenation process. Koenig pleads with the senile Guardian, but an accident forces the Alphans to retreat. Two rejuvenated women, called "A" and "B," emerge; "A" votes to save Alpha, "B" votes against.

Plot & Narrative Arc

The episode opens with the Moon struck by increasingly powerful shockwaves arriving every twelve hours, traced to deliberate explosions on a neighbouring planet. Commander Koenig, Maya, and Captain Carter depart in an Eagle to investigate. On a nearby moon they discover balloon-shaped structures and a cavern of spherical machines that communicate through spatial charts.

When Koenig sketches the Solar System, the machines identify his origin and explain that their organic Masters are sealed in chrysalises awaiting rejuvenation. The ruling Guardian is too senile to act, and Carter's attempt to halt a moving chrysalis nearly suffocates the entire crew. Koenig forces a hearing by threatening the Eagle's lasers.

Two female Masters emerge and vote on Alpha's fate: "A" favours mercy, "B" opposes. The deciding vote falls to the Guardian's brother, who sides against the Alphans. Yet Maya's calculation that a delayed explosion would push the Moon beyond the Eagle's range ultimately saves everyone, as the final shockwave is mysteriously weakened.

Production & Filming Logistics

Carrying the working title "The Chrysalis A-B-C," the episode was shot over thirteen days at Pinewood Studios during June and July 1976. It formed part of Series 2's "double-up stories" strategy, in which scripts were deliberately written to sideline different members of the regular cast so that two episodes could be filmed simultaneously on separate stages.

This scheduling approach was designed to prevent the over-time and over-budget problems that had plagued Series 1. "The AB Chrysalis" was shot in tandem with "Catacombs of the Moon," and to accommodate this, Dr Russell received a reduced role while Controller Verdeschi was written out entirely—both characters carried major parts in the companion episode. A notable technical detail: the bouncing motion of the fibreglass voice-probe props was created by filming them at high speed and then reversing the footage. The actor playing the Guardian's brother, David Sebastian Bach, is a five-times great-grandson of the composer Bach.

Critical Reception & Legacy

Critics have largely embraced the episode, with several singling out the spherical voice probes as a standout invention. TV Zone magazine hailed it as "great stuff" and credited it with restoring the mystery and enigma that had defined the show's first series. Reviewer Richard Houldsworth called the probes simply "a joy," while SFX appreciated the unexpected turn of the ending and awarded an A-minus grade. SciFiNow.co.uk went further, naming it "perhaps Series 2's finest hour" and praising both the refreshingly unorthodox portrayal of the Masters' culture and the tight, clear storyline.

Not every voice was positive: DreamWatch Bulletin dismissed the episode as having "very little going for it" and gave it a modest five out of ten. John Kenneth Muir, however, ranked it above Barwick's other script "One Moment of Humanity," lauding the alien world's non-Earth-like atmosphere, the machines' use of maps and shapes to bridge a language gap, and the unforced character humour. He also felt Landau's performance brought additional depth to Koenig's character, though he found the final communication device a slight strain on credibility.

Worldbuilding & the Masters' Civilisation

The episode constructs a strikingly alien society that breathes chlorine and dwells in an underground habitat beneath a planet with many moons. Rather than dying, the aged Masters enter chrysalises from which they later emerge rejuvenated—a concept the working title "The Chrysalis A-B-C" hints at. Their governance operates through a voting system in which awakened Masters cast individual ballots; in this episode, two women designated "A" and "B" (names the Alphans are told are untranslatable) vote on whether to spare Moonbase Alpha, with a third being serving as tiebreaker.

The ruling Guardian, by the time the Alphans arrive, is senile and sealed in his chlorine-filled chrysalis, rendering him unable to respond to Koenig's plea. The civilisation's technological side is embodied by the spherical voice probes—sentient machines mounted on stands that communicate through maps and shapes, eventually recognising Koenig as an Earthling when he sketches the Solar System. The planet's moons feature balloon-shaped buildings, and the nearest one holds the probe cavern where first contact occurs.