Zastros 9 was a planet that the Doctor's TARDIS landed on instead of Zastros 8 as intended, after the Nathemus interfered with the ship. It was not peaceful like its counterpart, as it was a totalitarian state policed by flying lizards.
Here, Melanie Bush was chased by these lizards while riding a battery-powered vehicle that she compared to a skimmer. The Sixth Doctor tried to contact her through its communication device, but had trouble getting reception. The vehicle's battery started dying and the lizards were able to catch up to Mel and and damage her ride. The Doctor, unable to teleport Mel back to the TARDIS, instead telported himself in the "skimmer" and set off the ejector seats, which used retrorockets to land them safely by his parked TARDIS. The two then promptly left the dangerous world. (AUDIO: The Brink of Death)