By Death Divided is the 14th book in the Thackeray and Ackroyd Series by Patricia Hall.
"Rage overtook him like a foul fog, filling his mouth with bile and squeezing his chest like a vice, forcing breath from his lungs with a harsh rattle. There was never any warning. One moment he was calm and in control, and the next filled with this murderous madness, which he only half-remembered after it had abated."
Caught by the current, her body tumbles this way and that in the black waters of the River Maze, dragged inexorably forward, her long dark hair trailing out behind her. For days she continues on, unseen, making a lonely passage through villages and marshes, until, at last, her journey comes to an end in a tangle of debris washed down with the flood waters.