From publisher blurb:
Magi study the hidden signs in the stars, in dates, dreams, and the movements of both smoke and fire. They understand that time moves not in a straight line, but rather in a great circle encompassing numerous aeons before all that is passes away only to return and repeat itself. Most creatures, unaware of this cosmic cycle, live the same life over and over again, but not the Magi.
Through their art, Magi read between the universe's lines in order to divine what is both the past and the future at the exact same moment. Armed with this knowledge, Magi can exert subtle but real influence on events, changing what was to come.
The Magus is a new character class for Swords & Wizardry. Also included are 12 new spells.