Into the Land of the Unicorns by Bruce Coville

One unicorn dwells on Earth.
Hundreds fight in Luster.
Their legends are recorded in
THE UNICORN CHRONICLES

Into the Land of the Unicorns
As each chime sounds, Cara climbs faster up the steep bell tower. Eleven! She must be on the roof when the next bell tolls. Twelve! With a deep breath, and only half believing she will survive, Cara jumps off the church roof and into Luster, land of the unicorns.

In Luster, Cara meets many wonderful creatures, but the most magnificent of all is Lightfoot, a rebellious young unicorn. Cara's band of friends comes to include a hairy creature named the Dimblethum and the monekey-like Squijim. Together, they set out to reach the Unicorn Queen before the mysterious man who is following them does - to prevent the destruction of all unicorns forever.

"Coville weaves traditional unicorn myths into his accessible fantasy...[with] an ending that hints at the next adventure." Booklist