Enter the Whisperer

"In Luster, the world of the unicorns, a strange new menace arises! Beloved, the great enemy of the unicorns, has stolen one of the Queen's Five, the powerful amulets that allow a human to enter Luster. By combining her own magic with that of the amulet, Beloved hopes to open a gate between the worlds – a gate that will allow her Hunters to launch a full scale invasion. At the same time Grimwold, Keeper of the Unicorn Chronicles, comes upon hints of an ancient story that may hold the key to survival. Reluctantly, the Queen sends Cara and Lightfoot on a perilous mission to recover this story. On Earth, Cara's father begins a desperate quest of his own, a search that begins with one of the strangest bargains ever made. And deep in Luster's forest, the mighty Dimblethum is tormented by tempting whispers from what may be the greatest menace of all." --Amazon.com.