As he unpacks his tool kit at an access panel near one of the windows, he fails to notice a sphere of orange light materialising above the lunar horizon.

Before anyone can react, the Main Mission staff are knocked off their feet by a tremendous jolt—a beam of orange light has reached out from the sphere and enveloped the Moon.

The fact that all but four Eagles are non-operational and the main generators show no sign of damage but are only putting out minimum power indicates that the sphere's occupants have purposefully compromised Alpha's defences.

Also, his optic nerve had been reconfigured to function like a high-speed camera and the processing speed of his neuronal system having been increased a thousandfold.

During this, Bergman's suspicions are confirmed as the viewer is taken into the sphere where unseen entities reside in a black void, surrounded by swirling coloured light and melodic sound.

Halfway to the downed Eagle, Koenig's party is ambushed; a ball of orange light approaches and Helena is compelled to walk into it.

Koenig wants to make another attempt to penetrate the sphere; he proposes to Bergman that in order to defeat the Tritonian force-field effect, they need to radically increase the strength of their Eagles' standard anti-gravity screens.

Before being rendered unconscious by the mounting g-forces, Koenig manages to switch the instruments to automatic and Morrow brings them safely back to Alpha.

During this activity, a ball of light drops down to the Moon's surface and, at an Alpha airlock station, deposits a smiling Helena.

Moving to Bergman's quarters, the professor finds a possible reference to the Tritonians as the 'Eyes of Heaven' in the Pyramid Texts of the Old Kingdom of Ancient Egypt, revealing their long-term observation of Mankind.

Koenig forwards a report from Kano that the malfunction of a computer memory cell disabled the Triton force-field for the thirty-two seconds required for the system to correct the error.

A plan is formulated to intentionally jam twenty-five key memory circuits in Computer, negating the force-field for the thirteen minutes required to fly to the sphere.

Koenig hopes to persuade the Triton probe that, with the death of its home world, its function is obsolete, and to release Helena and the Moon.

Against expectations, Elms (who was producer Sylvia Anderson's son-in-law) thought he could improvise a score with the musicians the day of recording, as he could neither read nor write music.

To avoid a walkout, Willis stepped in, hurriedly set some of Elms's themes down on paper, and conducted the musicians himself.

[2] Barry Gray wanted the music to be in the style of Maurice Ravel; Elms and Willis's final product is more reminiscent of the rock idioms of the day of the bands Deep Purple, Emerson, Lake & Palmer and Yes.

(Many themes from this movie were reworked into "Ring Around The Moon" and his subsequent stories for the series "Missing Link" and "Alpha Child".

As the theme of the episode is the foundation of science and whether the human condition can be understood from the point of rationality alone, it seems somewhat unclear why they changed from Uralt to Triton.

[3] In general, the story seems to be about the relationship between power and knowledge, and, to a large extent, appears to be a visualization of some of Michel Foucault's main writings.

Some have compared the visual style to the German Expressionist cinema, others have found parallels in the French and Eastern European Theatre of the Absurd.

[4] From a visual point of view, the episode could perhaps be seen as a paraphrase over the final third of 2001, consisting of the psychedelic "journey through time" sequence and the study of the astronauts M. C. Escher-like reflections on his own self-image.

Although he writes that "the plot itself is undeniably a little thin", he praises director Ray Austin's "stylised use of sound" and the lighting particularly inside the Tritonian sphere which "imbue the sequences with a sense of tension and atmosphere – the aliens are heard but never seen".

The probe's home of Triton was no longer a planet two million light-years from Earth, but the moon of Neptune, which in this narrative, had gone missing some few years before 1999.

Bergman also creates the anti-gravity shield specifically for the purpose of penetrating the Triton ship's forcefield, having gained the knowledge required to perfect the technique from the atomic-waste explosion earlier in the novel.