The Hunter Chronicles Series by E.J. Patten

Eleven years ago, Phineas T. Pimiscule rescued his nephew Sky Weathers in the town of Exile. Since then, Sky studied traps, puzzles, science, and the secret lore of the Hunters of Legend, believing it all a game, while his parent and uncle sacrificed to hide him. On the eve of Sky's twelfth birthday and his family's return to Exile, Phineas disappears. To find him, Sky joins ragtag teen monster hunters whose weapons are made out of garbage and know even less than he does... moreEleven years ago, Phineas T. Pimiscule rescued his nephew Sky Weathers in the town of Exile. Since then, Sky studied traps, puzzles, science, and the secret lore of the Hunters of Legend, believing it all a game, while his parent and uncle sacrificed to hide him. On the eve of Sky's twelfth birthday and his family's return to Exile, Phineas disappears. To find him, Sky joins ragtag teen monster hunters whose weapons are made out of garbage and know even less than he does. If Sky can't solve the riddles his uncle left for him within two days, Exile will burn. Who is Sky and why does everyone want to kill him? less

Sky thought he had problems before, when his uncle disappeared, his family moved to an odd new town, and he kept the world's deadliest monster imprisoned. But now, the entire Hunters of Legend are coming to Exile to kill him. Turns out he needs the same friends that he kept in the dark to keep safe, to stop an unspeakable evil from wreaking havoc on the world.