In the flashback to Edwin's death, the title card places the date as "Edwardian England 1916". The "Edwardian" era refers to the reign of King Edward VII. Therefore, the Edwardian era ended 6 years prior to the date given, with the King's death in 1910.
In the closet of the Dead Boy Detective Agency's London office is a copy of the board game "Clue". In the UK, this is sold as "Cluedo", seen behind them at around 20:23.
As in many shows filmed in Canada but set in the US, the ferry to Port Townsend (a real city in Washington State) is a BC Ferries ship, rather than a Washington State ferry.