A brilliant leader, a renowned strategist, a talented moderate in a bigoted age:  James Graham, the Marquis of Montrose, is a man of great charm and steadfast loyalty.    Devoting his life to King Charles I leads him to reluctant involvement in national affairs:  to intrigue, violence, treachery and battle.     With all Scotland almost in his grasp, his most hated enemy defeated and discredited and England and Oliver Cromwell next on the list, Montrose looks set to triumph.  But that is to reckon without the hand of fate . . . 'Through his imaginative dialogue, he provides a voice for Scotland's heroes' Scotland on Sunday