Kane Chronicles by Rick Riordan 2 Books Set Collection, The Serpents Shadow...

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The Serpent's Shadow

He's b-a-a-ack! Despite their best efforts, Carter and Sadie Kane can't seem to keep Apophis, the chaos snake, down.
Now Apophis is threatening to plunge the world into eternal darkness, and the Kanes are faced with the impossible task of having to destroy him once and for all.
Unfortunately, the magicians of the House of Life are on the brink of civil war, the gods are divided, and the young initiates of Brooklyn House stand almost alone against the forces of chaos.
The Kanes' only hope is an ancient spell that might turn the serpent's own shadow into a weapon, but the magic has been lost for a millennia. To find the answer they need, the Kanes must rely on the murderous ghost of a powerful magician who might be able to lead them to the serpent's shadow . . . or might lead them to their deaths in the depths of the underworld. Nothing less than the mortal world is at stake when the Kane family fulfills its destiny in this thrilling conclusion to the Kane Chronicles.

The Throne of Fire

Ever since the gods of Ancient Egypt were unleashed in the modern world, Carter Kane and his sister, Sadie, have been in trouble. As descendants of the House of Life, the Kanes have some powers at their command; but the devious gods haven't given them time to master their skills at Brooklyn House, a training ground for young magicians. And now their most threatening enemy yet--the Chaos snake, Apophis--is rising. If they don't prevent him from breaking free in a few days' time, the world will end. In other words, it's a typical week for the Kane family.

To have any chance of battling the forces of Chaos, the Kanes must revive the sun god, Ra. But that would be a feat more difficult than any magician has ever accomplished. First they have to search the world for the Book of Ra, then they have to learn how to chant its spells. Oh, and did we mention that no one knows where Ra is, exactly?