Three naval cadets accidentally get possession of a secret diary that was stolen from Bestuzhev, a vice-chancellor of Russia. If this diary ever gets abroad, the consequences for the country would be grave. The cadets are trying to return the papers to their owner, but there are others who want to get the papers...

In the second movie the Naval Cadets are guarding the princess coming from Germany to marry a Russian prince.

There is a seven-year war, Russian soldiers are forced to fight for the interests of France and Austria against Prussia. The midshipmen continue to selflessly serve the Motherland. One is on an expedition, the other is at court, and the third is sent to Venice to hand over a jewelry box. In fact, there is a message in the box, on which the future fate of Europe and Russia depends!

Crimea, 1787. Despite the Manifesto of the Russian Empress Catherine and the Kuchuk-Kainardzhi peace treaty, which forever united Crimea with Russia, Europe continues to weave intrigues, trying to break this sacred union. In the undercover struggle, all methods were used - from shameless gossip, dark rumors and false articles in newspapers to dirty manipulations with the illegitimate son of the empress sent to Europe for training - Alexei Bobrinsky, a passionate gambler and brawler. This weakness was cleverly exploited by international intriguers. Catherine instructs her faithful friends, the midshipmen, to cut the knot of the conspiracy ... Together with the fathers, their grown-up children, Shurka and Alexandra, go into battle.

The action of the film begins in the Crimea in 1787. Representatives of the Western powers once again begin their intrigues against Russia, but the main characters, former midshipmen, who have already reached a respectable age by this time, and their adult children, stand up to defend their homeland. They have to sail to the Crimea from Malta and there take part in the war with Turkey; in particular, to take part in the battle of Kinburn under the command of Suvorov.