What is the main conflict in The Ruby in the Smoke by Philip Pullman?

'The Ruby in the Smoke' is a mystery story set in Victorian London. Sally Lockhart's father has just died and she has received a mysterious letter telling her to seek out Marchbanks and to avoid 'The Seven Blessings.' Sally begins to investigate and is soon drawn into two dangerous mysteries, one revolving around a much-desired Ruby, and the other concerning her father's death. By the end of the story, with the help of new friends, she manages to solve both mysteries.