It was nice to read a historical fiction set in Prussia at the start of the 1800s with the possibility of Napoleonic invasion ever present. This debut novel by a husband and wife team (Michael Jacob and Daniela de Gregorio) is well-written, and has some evocative phrasing. However I didn’t feel this quite set the atmosphere, being perhaps a little too obvious at times. Also, the reason for the hero’s presence suffered from having a fairly weak foundation. The plot itself was satisfying enough but the book would have benefited from being 100 pages shorter, being somewhat laboured at times. The presence of Immanuel Kant was interesting – and helps explain the title – but the resulting central plot line was not strong enough.