This is book 3 of the "Young Wizards" series.

This note contains spoilers for the book.

 

Third of the Young Wizards series.

Nita's younger sister Dairine is a wizard too. She finds her wizardry in software that comes on their new Apple computer.

Dairine's ordeal takes her very far away, to a planet that turns out to have been a setup by the Lone Power. It's a planet of computer life, formed by layers of lava flow.

Dairine helps them make mobile units, and eventually lets them read her entire mind (to understand "slowlife" better).

Nita and Kit have set out after her, trying to trace her travels. Picchu, the macaw familiar of the local senior wizards, goes with them (and makes sense nearly all the time; apparently something serious is afoot).

They do find Dairine, just about when things are coming to a head with the Lone Power. Dairine is winning, but a little kick is needed for a perfect conclusion. Which they get. Picchu (having been killed earlier by the Lone Power) comes back in her true form as the Defender, mythological source of the Archangel Michael, Athene, Thor, and Prometheus, among others. Complete with sword that flames with the light of the perfect universe. The Lone Power is her brother, and she and the rest have grieved ever since it set out alone.

They actually convince the Lone Power to accept membership in the Powers again, and go back home with the Defender.

In what feels suspiciously like the author saying "Oh my god, what have I done? How can there be stories after this?", on the way out the Lone Power warns the wizards that there are copies and influences left behind, and as he has done evil, they will continue to do so for a while.