A Calculated Magic(1995)
(The second book in the Logical Magician series)
A novel by Robert E Weinberg
The Logical Magician returns in an outrageous battle between math and myth. Jack Collins is in Las Vegas, but he won't be spending much time at the dice tables. His boss, Merlin the Magician, has given him a mission: save the modern world from the Old Man in the Mountain, who plans to unleash a deadly biological plague.
Used availability for Robert E Weinberg's A Calculated Magic
February 1995 : USA Mass Market Paperback
August 1995 : UK Paperback