HIDDEN AGENDA. Porter, Anna. Toronto, Irwin, c1985. 280pp, cloth, $19.95, ISBN 0-7725-1513-1. CIP Grades 11 and up Reviewed by Joan McGrath Volume 13 Number 6 1985 November One does not usually think of publishing as a business fraught with danger, other than that posed by threats from the odd impassioned author or the occasional lawsuit. But when a successful Canadian publisher falls, or is pushed, to a horrible death under the wheels of a Toronto subway train, journalist Judith Hayes, his friend and admirer, refuses to believe the official verdict of suicide. Her half-hearted efforts at investigation are discouraged by both the police and the dead man's family, who have all but convinced her that she has been overreacting to the tragedy, when a second publisher is murdered. The two crimes, she is certain, are somehow connected. Judith and her friend Martha Hillier, a New York editor, are two unlikely but likeable sleuths, and their activities stir up a maelstrom, while bringing to light a conspiracy of stunning proportions. Slick and readable, this high-gloss detection owes its lustre to an equally glamorous author's expertise in the field she has made her own,Canadian publishing. Joan McGrath, Toronto Board of Education, Toronto, Ont.