The story features actor Roger C. Carmel voicing an uncredited reprise of his live-action role as Harry Mudd.
The starship Enterprise receives orders to arrest Federation outlaw Harry Mudd, who is accused of selling fake love-crystals.
[Motherlode] After convincing Nurse Chapel to use a love-crystal to win the affection of the Vulcan Science Officer, Mr. Spock, Mudd abducts her, steals a shuttlecraft, and escapes to a rocky planet.
The four are beamed back to the Enterprise, where Spock notes that the love-crystals' short duration and after-effect of enmity make them of little value, and Chapel records a confession of Mudd's misdeeds since his escape from the android planet so that he can be returned to rehabilitation.
[1] A 2018 Star Trek binge-watching guide by Den of Geek, recommended this episode for featuring the trio of characters Kirk, Spock, and Bones of The Original Series.