Wilson's Creek was one of the major battles fought west of the Mississippi (along with Pea Ridge, Prairie Grove, etc.).
The book begins much earlier than the Civil War, discussing events in Missouri, starting with the Louisiana Purchase. The book notes that (Page 2): "The road that ended in the Battle of Wilson's Creek was a long one--thoroughly enmeshed in the history of the continent and the pressures that accompanied the development of a new nation." Of more immediate relevance, the tension in Missouri before the outbreak of the Civil War is described.
As war broke out, those tensions increased. A central figure was the Union Brigadier General, Nathaniel Lyon. He worked to keep Missouri from falling into Confederate hands.
The battle at Wilson's Creek featured some intriguing figures. Fellow general Sterling Price (Old Pap) was also involved. Heading the Confederate forces was the colorful general, Ben McCullough. One of Lyon's lieutenants was Franz Sigel, who underperformed in many battles (including this one).
Lyon's troops were outnumbered. Despite that, he tried a tricky envelopment maneuver. Not surprisingly, it failed, leading in the end to the defeat of the Union troops. Sigel's colorful escape is nicely described. The book concludes by looking at the implications of the battle. An appendix with the order of battle for the two armies is provided, too.
A little brief and not quite as detailed as Piston and Hatcher's book but still a good overview of the first few months of the Civil War in Missouri. Although I don't understand the purpose of using the first two chapters to cover the Bleeding Kansas era.