Five short stories of the interplanetary hunters Gerry Carlyle and Tommy Strike visiting Saturn, Neptune, Venus, Almussen's Comet and Jupiter as they search for alien species for capture and return to Earth.

Tommy Strike and Gerry Carlyle stalk the monstrous Whip, suffer under the onslaughts of the Whiz-bang Beetles and track the huge Shovel-Mouth on Venus. On the fifth Jovian satellite, they meet the fire-breathing Cacus. The hunters meet Shaggies, Goras and the amazing, tunnel-boring Rotary Mole on Triton, satellite of Neptune. On Almussen's Comet, they battle the three-headed Hyclops and the intelligent, extra-Solarian Protean.