Intrigues - Mercedes Lackey

Magpie is a thirteen-year-old orphan chosen by one of the magical
Companion horses of Valdemar and taken to the capital city, Haven, to
be trained as a Herald. Like all Heralds, Magpie learns that he has a
hidden Gift-the Gift of telepathy. But life at the court is not without
obstacles. When Mags is "recognized" by foreign secret operatives whose
purpose is unknown, Mags himself comes under suspicion. Who are
Magpie's parents-who is he, really? Can Mags also solve the riddle of
his parentage and his connection with the mysterious spies-and prove
his loyalty-before the king and court banish him as a traitor?