High Wire by Charles Ogden
When a very bizarre circus comes to town in the dead of night, it brings with it caravans of strange and wonderful entertainers. Edgar and Ellen soon find kindred spirits among the fire-eaters and escape artists, but will the twins themselves join the circus as it leaves town (and avoid the wrath of Heimertz)? In this topsy-turvy world of smoke and mirrors, nothing is quite what it seems...