The Order of Excalibur - Reich Britannia

The Order of Excalibur - Reich Britannia is a fantasy novel for young adults set in a parallel universe in the early 1940s, where Germany has invaded and occupied Great Britain. This was one of the possible futures shown between the standing stones of Merlin's Ring of Fate that has now become reality, once the stones were materialized by Canadian teen wizards Nick and Ginny. Nick and Ginny are initially separated in a deadly nightmare world before being recruited by the British Resistance and relearning of the previous reality, risking their lives to alter the course of events.
They are also opposed by powerful German wizards in the Paranormal Division. Following an assassination attempt on the life of the German governor, security is tightened and many Resistance members are killed. With time running out before the reality of German victory becomes permanent, Nick and Ginny must find a way to bring back the Ring of Fate and put history back on track, before it's too late.