The Pentallian was mining the sentient star Torajii. When Martha Jones arrived onboard with the Tenth Doctor in the TARDIS, he was attracted to her. While trapped in an escape pod and thinking they would both soon die in the fires of the star, Martha reciprocated Riley's sentiments.
Several months before the incident, Vashtee first met Erina Lessak in a coffee house her family owned on Torajii Alpha. Physically attracted to Vashtee, Lessak befriended him and joined the Pentallian as a trainee engineer. (PROSE: 42 Prologue)