«The Outsorcerer's Apprentice» by Tom Holt

A happy workforce is a productive workforce.

At the moment, the Wizard's employees are neither. The goblins are upset with their working conditions, the dragonslayer has thrown a hissy fit over his medical insurance (or lack thereof) and everyone is upset about the terrible canteen coffee.

Yet the Wizard hasn't got time to worry about revolution in the workplace - he's about to see his brilliant business plan (based on entrepreneurial flair and involving one or two parallel worlds) disrupted by a clueless young man.

Side effects may include a huge hole in the fabric of reality.

This is almost certainly going to be a bad day at the office.