Go Saddle the Sea — Joan Aiken

Across the stormy sea, destiny awaits....
Felix Brooke, the orphaned son of an English soldier and an aristocratic Spanish mother, has been raised in his grandfather's strict, loveless household in Villaverde, Spain. When Felix gains possession of a letter that contains a clue to the whereabouts of his father's family, he gladly runs away to England to pursue the trail.

But there are times when Felix wonders if he'll ever reach his destination at all. Along the way he is accused of murder, captured by a band of gypsies, and discovers a shocking plot against his own life. Yet through it all, the resourceful Felix remains determined to find his place in the world.