Raven
Raven is an assassin for hire and will do what needs to be done in order for him to earn money. He has a heart full of vengeance and is genuinely angry at the world as it is. He has a harelip but is otherwise looked upon as a normal person. He grew up as an orphan, as his mother committed suicide after his father was hanged for murder.
Anne Crowder
Anne crowder is engaged to a man named Jimmy Mather, who happens to be the detective leading the investigation and hunt for Raven. She happens to be on the same train as them, and they befriend each other. She believes in justice and wished Davis dead, which is how Raven and her end up working together.
Davis / Cholmondeley
Cholmondeley was Raven's customer, and hired him to kill a government worker, in hopes of starting a war. Instead of paying Raven his earned money, he gave him stolen money that was useless as they knew it was stolen. This is why and how Davis and Raven initially became enemies.