Spirits
Spirits, or ghosts, play an incredibly important role in The Empty Grave. Each of the spirits in the novel, some who are named and some who are unnamed, are the main antagonists of the novel. They haunt the people of London—their homes and their businesses. Not only do the spirits haunt the people of London, but they also work against the kids in Lockwood and Co., who aim to stop the threat that the spirits pose to them and London more generally.
Bravery
Each of the characters in The Empty Grave exhibits tremendous bravery. The very nature of their work (investigating and confronting spirits and other evil spirits) is brave, and few people would even be willing to do what the kids in Lockwood and Co. do. There is a real possibility in their work that they could be seriously hurt—or more importantly, killed. But the kids in Lockwood and Co. act in a brave, curious, and energetic way, ignoring the danger they find themselves in along the way. Because without this bravery, their job couldn't be done well.
Family history
Family history is a frequent topic of discussion in Stroud's The Empty Grave. Throughout the novel, many characters discuss their family and how they came to be who they are. For instance, the novel explores the family history of a legendary psychic named Marissa Fittes. Fittes died years before the events of the novel, but her death (and the deaths and involvement of her ancestors and other families) changes London and the world more broadly. As the kids in Lockwood and Co. progress on their adventure, they also engage with Lockwood, who they hope to learn more about. They also hope to learn more about Lockwood's family history, which they think could potentially help them complete their adventure. It is only with Lockwood's family history, after all, that they can finish their mission.
