Who is Josh Newman from The Magician and what is their importance?

Josh Newman is the son of two archeologists and paleontologists. Due to this, Josh and his family has moved around a lot in their lives until recently when his parents took teaching jobs in San Francisco. Josh began what he thought was a normal job at a book shop that suddenly turned a crazy turn less than three days ago when a man, Dr. John Dee, stole a very important book from Josh's employer. Now Josh finds himself in Paris with a sister who has suddenly begun using magic.