Books in the Mysterious Secret Guardians series

The Secret Guardians completed their deadly mission in the London Underground. Now, they must rush to save the planet from total devastation. To do this, Sir Winston Churchill, Dr. Albert Einstein, hunky former MI5 agent, David Smythe, Dr. Raven "Bones" Wyndot, and Sophie the ghost Great Dane must crush formidable human and demonic adversaries.They dash from their HQ at the classy London Savoy and jet to Owl Mountain in Poland. The herculean task begins! Below the centuries-old Ksiaz Castle, in the blood-tainted bowels of the earth, hideous entities await. The Guardians must defeat the monsters and destroy the fabled Nazi Doomsday Machine. Time is a crumbling ledge beneath their feet. Soon, the earth may be reduced to smoldering rubble.