This Scepter'd Isle by Mercedes Lackey, Roberta Gellis

His vision was now back to normal and he saw the dark stains on the blade; he could not sheathe it as it was. He extended his arm and asked FitzRoy to find the kerchief in his sleeve so he could wipe the weapon. Instead the boy removed his own fine linen kerchief from his belt and held it out.
    "Take mine. It's wet already." As he said the words, FitzRoy's eyes widened. "And I guess I do need watching over. That man," he said, his voice now tremulous and unsure, "he was going to drown me."
    "What did he do?" Denoriel asked.
    "He pretended to be interested in my boat—he called it una barca —and when he came close, he pushed me into the water. And he was trying to push my head under when you yelled. He kind of jerked around and I went lower and pulled free. He kept grabbing for me, but mostly he was watching the fight so it was easy to keep out of his way. And when I thought he was going to stand up and join the fight against you . . . I threw two handfuls of muck from the bottom of the pond into his face."
    Denoriel burst out laughing. "Good for you, Harry!" Then he sobered. "I'm your fairy knight, true enough, and I am a good warrior, but I'm not all powerful. If you hadn't helped me . . . I would have been killed."
    FitzRoy nodded wisely. "Because fairies can't stand cold iron, and those men's swords were iron. Nurse told me about that too, but I forget the name of the story. I remembered about the iron though, how iron burns fairies. That's why I dragged the swords away from you."
    "Clever Harry! The swords were making me weak."
    "I knew that. That was why I hit the man in the back of the knee with the mast of my boat. You're magic, I suppose, but you aren't God. Only God is all powerful." The boy sighed. "But God's a lot like my father. He's far away and He must be busy with more important things than me." His eyes brightened and he smiled again. "I guess that's why there's fairies and fairy knights."
    Denoriel bent down and embraced the child quite fiercely. "Yes. That's why there's fairy knights, to make sure children are protected."
    FitzRoy hugged him back. "When he pushed me, I was afraid, but I knew you'd come. I've wondered ever since you came why I was so lucky as to get a fairy to help me. Now I know. Except . . . I don't know. Why should he try to drown me ?"
    "You didn't know them?" Denoriel asked. And when FitzRoy shook his head said, "How did they get past the guards?"
    "I'm not sure." The boy frowned. "I saw them come into the garden . . ." He hesitated and then said, "But you're right. I didn't hear them talk to the guards at the gate. I didn't think of that then because I was very annoyed with the men. I knew you wouldn't come if they were here. I know no one is supposed to know about fairy guardians, which is why you only come when I'm alone."
    "That's true, but we're going to have to confess that we are special friends. You see, you are going away—"
    FitzRoy clutched at Denoriel's hand. "I know. I'm to be lord lieutenant in the north. It won't matter, will it?" he asked fearfully. "If you're my fairy knight, and you have magic, you can come to me up north, too, can't you?"
    "Yes, I can," Denoriel assured him, smiling. "But we agreed I'm not all powerful. I'm not all knowing, either. I'll need to see the place where you are living in the north so that we can arrange where to meet or so that I can get to your apartment. I won't have the excuse of coming with my friend Boleyn."
    "Oh, yes." The boy nodded. "I can ask for you—not as if we've been friends all along, but because you saved me from those men. I can say I don't want to go to a new place if you can't come too."
    "We can try that first," Denoriel agreed. "If it doesn't work . . . don't worry yourself, Harry. I will find a good reason to visit Yorkshire . . . wool, probably. And once I am there, it is only reasonable for me to come to call. But until I can find a way to you, be careful. Don't be alone."
    "No, I—" FitzRoy