Black Mercury by Charlotte E. English

Son of a wealthy businessman, Caspar Goldstein has it easy — too easy. He's the star of the local racing scene, but while hobnobbing with his fans is fun, no amount of money or status can win him the Eisenstadt Autocarriage Cup. So when he stumbles over a new superfuel that could rocket him straight to the front of the pack, he can't resist appropriating a bit for himself. What could possibly go wrong?

Well… a lot, actually. Everybody wants to get their hands on a little black mercury, and Cas is in deep trouble. Pursued, hunted and forced into hiding, Cas needs all the help he can get. Luckily for him, he's not short of friends — but how can a crew of engineers, racecar drivers and talking pigeons hope to face down the deadliest of assassins and thieves?