This is a series that you want to read from the start to fully enjoy the character arc of Lucie, the state of London's ghost plague, and understand the different levels of ghosts. Lucie is extremely talented as a ghost hunter but unorthodox and empathetic toward them. She's also attached and attracted to Lockwood in a way that is more clear having read the previous books. In this story she's frustrated with Lockwood as he shuts people out of his life and keeps them at a distance. He always has but Lucie thought after he opened up about his sister's death he'd not go back to being the way he was previously. But old habits die hard and Lockwood crawls into his shell while Lucie tries to deal with her feelings of rivalry with the new hire.
The pacing felt a bit choppy as the team kept taking on what seemed like random cases, but eventually the direction becomes clear. When Holly joins the team, she and Lucie bicker at a tiresome rate and it is pretty clear a confrontation will happen. I just didn't expect it to happen like it did. Jonathan Stroud is good with surprises. The ghost in the bottle is sarcastic and adds humor to the story that balances the dark side of what is happening in London. He's like the djinni in the Bartimaeus trilogy. The horrors would be oppressive without his voice. He's also unpredictable because sometimes he is helpful, but usually he is doling out bad advice to Lucie. Like telling her how to kill Holly while on an assignment. Good fun with an ending that will make you scramble for book four.