The episode was adapted in the third Year One Space: 1999 novel The Space Guardians by Brian Ball, published in 1975. Ball's adaptation is true to the story, but some liberties are taken:  (1) Suffering from a bout of depression, Koenig has become a recluse after his experience on Zenno (as seen in "Missing Link").
The episode was reimagined in the third Year One Space: 1999 novel The Space Guardians by Brian Ball, published in 1975. Ball's rendition is faithful to the narrative, but some creative liberties are taken:  (1) Struggling with depression, Koenig has withdrawn from society after his experience on Zenno, as depicted in "Missing Link".