Andre Norton: Voodoo Planet: A duel of two cosmic magicians - a horrible death for the loser

The Time Traders II: The Defiant Agents and Key Out of Time

Catseye

Roadside Picnic

Clifford Simak: Hellhounds of the Cosmos

Worlds of the Imperium (Unabridged): optional

Darkness and Dawn

S. P. Meek: GIANTS ON THE EARTH

This is How You Lose the Time War: The epic time-travelling love story and Twitter sensation

Jack Williamson: Salvage in Space: To Thad Allen, meteor miner, comes the dangerous bonanza of a derelict rocket-flier manned by death invisible.

Star Flight

Storm Over Warlock

The Cosmic Junkman (Unabridged): optional

Dark Companion

Slaves to the Metal Horde (Unabridged): optional