The fearsome firebird - Lauren Oliver

In this third book in the exceptional Curiosity House mystery series
by bestselling author Lauren Oliver and mysterious recluse H. C.
Chester, four children must uncover the evil Nicholas Rattigan's newest
dastardly scheme, wage war with a rival freak show, and deal with a spy
who may have infiltrated their happy home.

Sam, Philippa, Thomas,
and Max have just started to recover from their capture and subsequent
escape from Rattigan. But the children's lives don't stay quiet for
long.

A slew of bank robberies is terrorizing the city. And when
Professor Farnum, the ringmaster of the museum's now immensely popular
flea circus, is charged with murder, the search for the real killer
uncovers a plot much bigger than any individual crime-a plot that can
only be the work of Nicholas Rattigan.