The Corsican Brothers

In the Citadel of Defranche twin brothers, Lucious and Lucien, are born to the count during a siege. A prophecy stated that when this occured the House of Defranche would fall. The same prophecy stated that the twins would restore their family on their 18th birthday. Trusting to the prophecy, Count Defranche entrusts his sons to his Captain of the Guard and his inventor and sends them in separate ships. The boys are given magic amulets to prove their identity when the time came.

Eightteen years later, the two brothers reunite on schedule. Captain Orlandi and inventor Benbimo tell the boys of their true heritage and put the final stages of their operation into motion. Adding to their motivation is Countess Isabelle Gravini who Lucien rescued from a runaway coach. She was on her way to the home of her new guardian, unaware that this was a trick into to lure her to the citadel of the villain.

The cartoon is an adaption of a novella by Alexandre Dumas, père first published in 1844. It has been adapted many times on the stage and in film since 1898.

The Corsican Brothers provide examples of the following tropes

 * And Now You Must Marry Me: Isabella thought Desotro was going to be her guardian. He changed his mind once she was safely trapped in his citadel.
 * Amplified Animal Aptitude: Orbo, Lucien's pet falcon. He's a scount, a messenger, and when his owner screws up the plan to retake the citadel, he quickly adapts it by stealing the keys to Isabelle's room so she can open the gates and let the milita in. It verges on Hypercompetent Sidekick.
 * Big Bad: Count Desotro, the man who took over the Defranche Citadel and killed the protagonists parents.
 * Distressed Damsel: Isabelle is introduced to the audience in a runaway carriage and held captive by the Big Bad for most of the story.
 * Distressed Dude: Loucis is introduced to his brother by way of angry boar. Both he and Lucien are captured by Desotro later on.
 * Evil Is Not a Toy: Desotro invokes an ancient demon with the two amulets and tries to force it to obey him. It laughs in his face and zaps him with fire.
 * Evil Plan: Desotro has three distinct plans.
 * Take over the Defranche citadel. Why he does is this not explained. He even calls it a 'miserable place' after the timeskip.
 * Force Isabelle to marry him; for reasons that can't be stated in a kid's show.
 * Take Over the World once he gets the amulets
 * Large and In Charge: Desotro is tall and broud shouldered; his minions are scrawny.
 * MacGuffin: Averted. Desostro didn't know the amulets existed until the third act. The usual 'hero and villain fight' is short and spectularly one-sided. In any case they play a small role.
 * Neutral Female: Averted. The first thing Isabelle does when she frees herself from her room are 'I should open the gates so the miltia can get in'. She sneaks past the guards and does just this.
 * Nice Job Breaking It Hero: Once by each twin.
 * Lucien sneaks off in the middle of the night to inflitrates the castle and open the gate. He doesn't tell anyone. The milita hasn't been gathered yet. All he accomplishes is getting captured and altering Desotro to a possible attack. he doubles the guard.
 * Lucius is sent by Bambino open the gate and is explicitly told not to look for his brother before he does this. He promptly forgets as soon as he realizes Lucien is being tortured. Shortly after that he's captured and Desotro gains the second amulet.
 * Screw This I'm Outta Here: Desotro's soldiers flee in mass after recieving a beating from peasents with pitchforks. Bambino even holds the gate open for them.
 * Supporting Leader: Orlandi has far more experience as a fighter than either brother and is the one leading the milita.
 * Smooch of Victory: Downplayed. Isabella gives Lucien a hug of victory.
 * Synchronization The twins feel each other's pain. They can also psychically discern the other's location.
 * Useless Protagonist: The two brothers try but ultimately all they achieve is helping Desostro. In retrospect, they should have stayed put and let their foster fathers take care of everything.
 * What the Hell Hero: Averted. Neither brother is called out for endangering the plan to retake the citadel.