Why would one family choose to fight for the enemy of the British Empire, while another defends it?

It’s 1915. The Great War has descended into horrific trench warfare with the great nations fighting over inches of European ground. In the Middle East, the war is between the British Empire and the Ottoman Empire, allied to Germany. Caught in the middle of this Middle East war are two families of spies — the Bankrofts, who support British operations in Mesopotamia, and the O’Connell family, on the side of the German and Ottoman operations. Both families trained in the mystic arts, mesmerism and intelligence tradecraft in British India, but one chose patriotism and the other, treason. The intelligence chess game between these two families places them at even greater risk as their tribal allies switch sides and fight for their own reasons.