A union raiding party, that was sent into Loudoun County to eliminate Confederate partisans, was ambushed by Mosby's Rangers near the village of Harmony.

After inflicting light casualties on the Federals, the Rangers were unable to drive off the numerically superior and better equipped force and were compelled to withdraw.

Unsure of the strength of the opposing force, Mosby lead his Rangers approximately 1 mile (1.6 km) southeast of the village.

The 12th Pennsylvania soon came upon the Wiltshires men, and taking them to be an isolated band of partisans of the nature that the Federals had been fighting with since entering Loudoun, immediately charged.

Wiltshire's force broke into retreat until they reached the woods where the rest of the Rangers were concealed, at which point they suddenly turned around and counter-attacked the Federals.