Hunt for the Nighthawks

It's Jake and his friends versus the Nighthawks . . . and the Nighthawks will stop at nothing to get what they want.
A thrilling middle-grade adventure of friendship and bravery, combining mystery, history and the supernatural. By the bestselling author of the Specky Magee series.

When Jake meets the ghost of a young Roman soldier, he is sent on a mission to recover stolen treasure from a group of thieves known as the Nighthawks.
It will take all their detective skills and courage, but Jake and his friends Tilly and Rabbit will uncover much more than gold and silver, and the stakes are higher than they could ever imagine.