The story takes place in the year 2363. The protagonist is Cadet Larry Stark, a 20-year-old, fresh graduate of the Space Patrol Academy who comes from a long line of Space Patrol commanders. As the story begins, he is embarking on the customary final training cruise on the interstellar ship "Carden". At the end of this cruise, he will be awarded a commission as officer of the Space Patrol. The ship makes the four and a half light-year journey to the star Alpha Centauri in a span of 15 days using the faster-than-light overdrive. The fourth planet orbiting Alpha C, an earth-like planet inhabited by dinosaurs, has been colonized 125 years earlier.