Once a murder has happened, to go back in time and prevent it might seriously mess with the timeline, and that is where the Time Patrol's Murder Squad comes in. They try not to kill anybody themselves, except in emergency defence of themselves or the timeline, but they are known as the Murder Squad because they are there to make sure the murders of the past happen.
Created in the far future, then sent through a temporal rift to the ancient past by the Chronomage Cara, the Circlet is an artefact designed to focus a mage’s energies when attempting to manipulate time.
All magic is suddenly gone. No mage can sling sorcery anymore. This upsets all empires and civilizations. It is soon discovered though, trough the combined work of mystics, scholars and dreams, that all the magic has been drawn into a single orb in a vast tower located at one of the poles. Whoever gets there first wins the greatest price in history, access to all the magic in the world. But who owns the tower?