Snakehead (Alex Rider, #7) by Anthony Horowitz

Splashing down off the coast of Australia, Alex is soon working undercover – this time for ASIS, the Australian Secret Service – on a mission to infiltrate the criminal underworld of South-East Asia: the ruthless world of the Snakehead. Faced with an old enemy and troubled by his own past, Alex is caught between two secret services, with no one to trust – and this time he needs all his wits to survive...