Flyte by Angie Sage
The evil necromancer DomDaniel has been disposed of, but something Darke is stirring. A Shadow pursues ExtraOrdinary Wizard Marcia Overstrand around, following her every move, growing stronger every day. Septimus senses something sinister is afoot, but before he can act, Jenna is snatched - taken by the most unlikely kidnapper. Septimus must rescue his sister but does not, at first, realise what he will be facing. 'Flyte is the second of Angie Sage's engaging and energetic novels about Septimus Heap ...We can't get enough. More, please!' The Times