The Unexpected Tale of the Bad Brothers (The Bastien Bonlivre Adventures) by Clare Povey

Bastien Bonlivre is in trouble again. His sworn enemy, Olivier Odieux, has escaped jail and is out for revenge...

Meanwhile, across Paris, fires are burning, and danger lurks at every corner. Who could be behind this?
As clues start piling up, Bastien and his friends Theo, Alice and the mysterious Mathilde must set off on a daring treasure hunt to track down the answers they so desperately need. Because if they don't find them, it won't just be Bastien who is in danger...but the whole of Paris too.