T. J. Andrews & Simon Scarrow 
Invader: Imperial Agent (4 in the Invader Novella Series) [EPUB ebook] 

The fourth novella in the gripping INVADER series, set in Roman Britain, AD 44, from Sunday Times bestselling authors Simon Scarrow and T. J. Andrews In the winter of AD 44, Rome’s plan to install a friendly king in the most hostile area of Britannia is facing a new threat. There are rumours of a traitor close to the new king, and a new enemy is gathering strength beyond the marshes. As the king continues with his plans to Romanise his subjects, Horatius Figulus, a junior officer in the Second Legion, is charged with training up the new royal bodyguard. But when a trap is sprung on the Roman army, a secretive Druid sect seizes power and takes the king hostage.Now Figulus must infiltrate the enemy ranks, release the king and track down the elusive leader of the Druids — before the whole of Britannia descends into bloody chaos…