(warning: minor spoilers!)
this won't ruin the book for you, but unless you want to know most of the plot in advance, i'd rather recommend not reading it.
frederich, poised on the brink of gaining a terrible power through violence, hesitates and is betrayed by his predecessor and mentor (daniel). sundered into three physically separate segments of self (signifier, signified, and referent / shell), frederich is forced to progressively relive (and thus recover) his own past. unbeknownst to frederich, daniel's spell of sundering / imprisonment also threw all four survivors of the antecedent violence into a temporal stasis and illusion of place. aided by a silent survivor of his acts of violence (elizabeth) and the spirit of a forest infused with sentience by the blood of his victims (the lord of white ash), frederich is brought to fuller awareness of his actions and the choice that forced him into his crucial hesitation and subsequent betrayal. when daniel, elizabeth, frederich, and the last crucial survivor of the ritual sacrifice (gabriella) are reunited, the full significance of the power he was poised to receive is revealed. frederich's interrupted decision is again set within his reach.