Voyage to the City of the Dead
Alan Dean Foster
 Scientists Eitienne and Lyra Redowl come to the planet Horseye to study the entire length the immense Skar River and its spectacular river chasm, the largest in the whole Humanx Commonwealth. On Horseye there are three separate sentient species, which all have different concerns about their planet. The Mai, traders from the river delta, are prepared to help the Redowls, but had their own agenda for doing so, for it was rumoured that at the head of the river was the City of the Dead and a great treasure. This treasure is eventually revealed to be not be material wealth, but an ancient artifact that is used to monitor the depths of space for an approaching evil.