Murder Imperial
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It is interesting to see how the more you read, the more you doubt everybody. All the people in the novel are hiding things and you never really know who they're really helping (or if they're helping anybody at all). Also, everybody has their own interests, so they may be helping somebody at one point and trying to make things difficult for them at another. This makes it difficult for Claudia to find the killer, but it also makes it difficult for us as readers to know who the bad guys are.
Claudia is also hiding something: her past. She is working as a spy for Constantine's mother to be able to find the man that killed her brother. All she knows is that the man had some sort of tattoo in his wrist but she soon learns that this just means that the man belongs to a certain group.
In the end you don't know how bad all the characters are, because while the most immediate problem is solved, half secrets have been revealed that are probably part of further novels (I haven't read the next books in the series, so I can't be sure, but it is strongly hinted).