Behemoth starts off pretty much where Leviathan ended: the Leviathan is making it's way to the Ottoman Empire with help from the Clanker engines. There is an uneasy truce between Alek's men and the British, but Alek and his companions are still basically prisoners. 
 There are more adventures, German threats (including a new Tesla cannon), anarchists, new allies and enemies, some secrets are revealed, and the stakes are raised. There are also fantastic mechanical creations and new beasties too. 
 Once again, the worldbuilding is phenomenal. Very good action sequences too. Alek is making more decisions regarding his life, and it's good to see a strong sense of responsibility developing here. Deryn is still keeping her secret. She's thriving as a middy (totally, completely kicks ass), but knows it will all be taken away if it is discovered that she is a girl. 
 I cannot wait for book 3.