The Whispering Skull by Jonathan Stroud

In the six months since Anthony, Lucy, and George survived a night in the most haunted house in England, Lockwood & Co. hasn’t made much progress. Quill Kipps and his team of Fittes agents keep swooping in on Lockwood’s investigations. Finally, in a fit of anger, Anthony challenges his rival to a contest: the next time the two agencies compete on a job, the losing side will have to admit defeat in the Times newspaper.

Things look up when a new client, Mr. Saunders, hires Lockwood & Co. to be present at the excavation of Edmund Bickerstaff, a Victorian doctor who reportedly tried to communicate with the dead. Saunders needs the coffin sealed with silver to prevent any supernatural trouble. All goes well-until George’s curiosity attracts a horrible phantom… Read more.