Heart is sure the small book she found in Lord Dunraven's castle holds the secret to finding a safe haven for her beloved unicorns, Moonsilver and Avamir -- especially after a village blacksmith tells her about a pair of ancient iron gates decorated with the same unicorn motifs that appear in the book. While she struggles to learn how to read, Heart must continue to protect the unicorns, as Lord Dunraven's men close in on them.