Felix, Net, Nika and theoretically possible disaster

Felix, Nat and Nick barely moved away from the fight with the gang of invisibles, but they only dream of a calm life. They find secret German bases from the Second World War and mysterious portals that the Nazis hid there. Where are they going? And why, when the children went through one of them, the world around became so ... outdated?
Felix, Net and Nick will have to visit the past and future, run away from special agents, defuse a bomb, explore the fourth dimension, defeat the elite detachment of the Nazis and save the world from the threatening catastrophe. Manfred artificial intelligence will help them in the form of a whole swarm of flying mini -bots.
Will they be able to cope with everything and return home alive? Is it possible to change the past? And if so, what cost?
For secondary school age