In the Garden of Iden — Kage Baker

In the twenty-fourth century, the Company preserves valuable works of art and extinct forms of life. It recruits orphans from the past, renders them all but immortal with drugs, hormones, and implants, and trains them to serve the Company down the long centuries. One of these operatives is Mendoza, sent to Elizabethan England for her inaugural assignment to collect samples of rare plants from the garden of Sir Walter Iden. Yet her quest is jeopardized by the presence of Nicholas Harpole, whose outspoken religious beliefs conflict with those of Queen Mary. His courtly manner penetrates Mendoza's trained, cool detachment, and stirs unfamiliar emotions within her. Now she must contemplate the prospect of her future--with a man she will long outlive.