This episode and the following one (Divergence (2005)) attempt to explain the makeup change in Klingons between Star Trek (1966) and Star Trek: The Motion Picture (1979), which had been semi-acknowledged as canon since the broadcast of Blood Oath (1994) and Trials and Tribble-ations (1996) in the 1990s. Some viewers had criticized the Star Trek: Enterprise (2001) producers for not depicting Klingons of this era as smooth-headed, as they had been in the Original Series. While some fans simply ignored the Klingon makeup changes in the various series and films, others had longed for an "official" explanation. The writers of Enterprise hoped their take would find a way of satisfying both points of view, while simultaneously telling an interesting story.
After years of speculation, this Star Trek episode finally explains the more human-like appearance of Klingons in Star Trek (1966). The disease in this episode leaves its Klingon victims without head ridges, a phenomenon that was acknowledged but not explained by Worf in Star Trek: Deep Space Nine (1993)'s "Trials and Tribble-ations (1996)" when he said: "They are Klingons, and it is a long story. We do not discuss it with outsiders". Moments before, Worf's crew mates suggested either genetic engineering or a viral mutation as causes for the difference; ironically, the actual explanation is a combination of both.
The Klingon dialogue heard in this episode was translated by Marc Okrand, the author of The Klingon Dictionary and many other titles on the Klingon language. Okrand created the Klingon dialogue for several of the Star Trek feature films. Okrand was consulted by episode writer Mike Sussman, who wanted the characters to speak authentic Klingon.
Harris sends Lt. Reed an address at which to meet him - 1044 Maple, San Francisco, USA, Earth. Maple Street in present-day San Francisco is in a residential area just south of the Presidio - quite consistent with the setting shown.
This episode features the first appearance of the Rigelians in Star Trek. They, like the Tarkaleans, had been mentioned but not seen in previous series.
Seth MacFarlane: The creator of Family Guy (1999), Ted (2012), and the Star Trek spoof TV show The Orville (2017) makes an appearance as Ensign Rivers.