Excellent read, but some paganism and mythological themes, and some violence.
Percy thinks he's a completely normal boy with a few school issues... until a very strange incident on a field trip. Soon, Percy learns that all the gods and creatures of Ancient Greek mythology still exist, and that he is actually the son of the sea god Poseidon. Percy and his friends Grover and Annabeth are sent on an epic quest to find out who stole Zeus's famous lightning bolt, and, ultimately, save the world.
Good guys are good guys and bad guys are bad guys, mostly. We are told that Percy once downloaded a school paper off the internet and turned it in. Some of the pagan gods' morals are questionable, but those gods are usually depicted as antagonists. A character thought to be good turns out to be evil.
Tons. All of the creatures from Ancient Greek mythology are real. Mount Olympus exists on top of the Empire State Building, and the Underworld, where dead souls go after life, is under Los Angeles. The true God is not mentioned, other than a wise centaur saying that God is not a topic that needed talking about (in the context of the conversation at hand), while gods are. At one point, Percy seeks guidance from an Oracle. He also has supernatural dreams.
While in the Underworld, Percy and his friends see a crooked televangelist about to be taken to the Fields of Punishment for his misdeeds. One can't help but feel this is a slightly cheap shot at Christianity.
There is a hint of relativism ("What's true for me may not be true for you.") when we are told that not everyone in the Underworld sees the same thing. Their experience may vary depending on their faith.
Being a fantasy adventure story, there is a good amount of fantasy violence. Humans are fought in practice battles, and monsters are defeated. Most of the monsters turn into dust at their defeat, and at one point a monster is said to "burst like a piñata". One character tries to kill another with a scorpion near the end.
Drug and Alcohol Content
The Greek god of wine, Dionysus, is shown to have been banned from alcoholic beverages by Zeus. (He drinks Diet Coke instead). Percy's stepfather drinks beer.
The premise behind the book is that the ancient Greek gods still take human form from time to time and have mortal offspring outside of wedlock. Thereafter, they mostly ignore their kids.
There is mention of some married gods, including Zeus, Hephaestus, and Aphrodite, commiting adultery with mortals or other gods. Hephaestus sets up cameras in an attempt to broadcast his wife's infidelity live to Mount Olympus.
Percy and Annabeth seem to like each other, but not a whole lot is made of it. On a field trip, Percy and his group look at unclothed Greek statues.
Crude or Profane Language or Content
Possibly a few uses of "h*ck," "d*rn," or "d*ng." Some insults in Ancient Greek are hurled around, but none of those translated into English are particularly rude. "Oh Styx" is an expression of frustration.
There is a reference to one of the characters "losing his pants", but only because the character in question is a satyr and removing his pants would of course reveal that fact. When Percy battles the Minotaur, the Minotaur shows up wearing nothing but his Fruit of the Looms.
The Lightning Thief is impossible to put down. Quick prose and realistic dialogue pulls you through the story. However, it is probably best read by stronger Christians due to some of the pagan themes.