The eponymous Kestrel, Juvalos Skleros Gerakis, aka Olaf Falco, owner of the ship Tuulihaukka (= kestrel, 'wind falcon'), a young man, returns from Viking treks to meet his parents at Arantila manor in southwestern Finland, and finds them slaughtered by the neighboring manor's fortune-hunter younger son and his greedy allies.

Meanwhile, a young noblegirl Aure 'Nukuttaja' (Sleepmaker) of Launiala manor from southwestern Finland, abducted after left unprotected by her family, leaves with her restless brother Lyy, to seek to the Varangian guard of the Emperor of Byzant.

They settle a household in Constantinople, where Aure gets fame with her natural ability to calm and soothe sick people with singing, thus the name Sleepmaker.

Afterwards, the Byzantine court sends Lyy ('Leo') and Aure to accompany an imperial princess Arete Dukaina to her future husband Doge of Venice.

The violent and greedy kinsmen and the enemies of her husband Fulbert, particularly Prince Gisulf di Salerno, cause Aure many unhappy and dangerous incidents in the following years.