Fourteen-year-old Will is the youngest cowboy on a Montana roundup in the early 1900s. As the youngest, his job is to keep the cattle and horses calm at night by riding around the herd and watching for dangers like wolves or bears. The rider who does this job is called a Nighthawk, and Will is very happy and proud to play this important role. Will has two constant companions who make his job a lot easier: his horse Ranger and his trusty harmonica. He also has a grumpy and intimidating boss in the Camp Cookie. When a sleepy Will makes a series of small mistakes that hold up the cattle drive, he expects to be punished by an angry Cookie, who usually thinks the young Nighthawk isn't worth his bacon. Instead Will discovers that there's more to Cookie than meets the eye and learns an important lesson.