In 1232 BC, Laodamia of Phoenicia, the Oracle of Delphi, is dying in Morocco. She gives her bronze cuffs to the Carthaginian General Adrastus because they activate the portal for the United. Laodamia is about to die, so makes the general her Secret Keeper and swears him to delivering boxes of secrets and marrying Adria. Fast forward to 1940, where the orphan Ian is mourning the death of the man with whom his mother left him before he ended up in the Delphi Keep orphanage. Ian has other worries-- England has entered the war against Germany and English children are being evacuated into the countryside. Ian gets involved in a scuffle with a German officer and a mistress at the school is injured, so he tries to get Eva, another orphan who travels through the portal and who has healing powers, to come help. He meets Argos, an ancient Phoenician solider who is sent with the oracles prophecy. Ian and his friends must work to solve this, but if the United leave Delphi Keep, they won't be protected, and only they can solve the riddle of the propehct, find and save the secret keeper, and help the English against the Germans. The prophecy
indicates that seven children will come together, and this book ends with only five having been found, so there is probably another book on the way.
Since this involves some mythology (as well as some French witches), fans of Rick Riordan might be interested. There is also a lot of World War II information; it reminds me a little of Ted Bell's The Nick of Time with it's journeying between two historical periods.