Luck was on the side of Canterlot, before the big royal wedding one of the Guards during shift accidentally found the secret entrance to the caverns underneath the Castle. Following cries of sadness led to the discovery of the real Princess Cadence. The guard took Cadence to above and managed to interupt the wedding just in time.
The imposter Princess Cadence had revealed herself as Queen Chrysalis of the Changelings. She led her swarm into invading the city and were only stopped when Shining Armor was able to use Princess Cadence's love for him to activate his shield spell to repel them. Once the threat was over everypony began getting to work putting things back together.
However Princess Cadence noticed something...
"Wait where is Twilight? I know she was on the guest list to be the best mare but I was kidnapped before she came. Where is she?" Cadence asked dread filling within her for the fate of her younger sister figure. While Twilight and Shining Armor's parents began to be worried about the whereabouts of their daughter others then had panic fill within them.
"Has anypony actually saw her yesterday after... you know..." Shining Armor asked facing the direction of Princess Celestia and her friends who all had faces of worry remembering what had happened last time they had saw her. They left her alone disappointed at her claims... which turned out to be true...
Twilight Velvet and Night Light stopped when they noticed the look on their son's face was the one he had when he had a worrying secret. However then entered Princess Luna who stated "I would be asking if I missed anything but it seemed that I did. Since I had not seen her in a while, I went to check on her in her room when I found this note on her bed."
Princess Luna had the note using telekinesis which Princess Cadence took from. She began reading it out loud:
Dear everypony
I am sorry about this, all the trouble I caused. With how Cadence had been acting during the preparations, casually dismissing the hard work of her friends and seeing her perform her spell on Shining... I guess I acted without thinking, especially since Shining had told me some evil was about. I will be going, I don't think I deserve to be around everypony. I wish everypony the best and I hope the next time we meet. I am sorry that I have decided to be a coward and not face everypony's disappointment and the consequences myself. I am sorry for everything, especially how I acted towards Cadence.
Sincerely Twilight Sparkle
Each word seemed like a stab in their hearts and the guilt kept on pressing higher, however there were accusatory looks from Twilight Velvet and Night Light, Shining realised he would have to explain what happened especially since his excuse to them was that he hadn't had the chance to see her since she had come to Canterlot. Cadence lowered the letter from her face and she had an unnatural smile on it.
"Explain now." Cadence calmly said still in her unnatural smile and Shining gulped. It would have been a much better if she had shouted angrily...
Once the ensuring explanation was made for what happened, Cadence made it clear that if they were going to be married then first they would have to find Twilight safe and that Shining WILL explain and apologise to her. Shining felt he had to do it anyway and Twilight's friends began leading the search themselves, feeling like it was their duty to find her and make things right. They began sending out posters and requests for information.
They searched for two years without luck, they had to go to their own lives while there was still squads looking for her as well as requests for information about her whereabouts.
Princess Celestia felt like she had failed to find one of the ponies that were the closest she had to a daughter. She should have been more alert about suspicious behaviour, especially since she knew there was something evil about.
However a new problem recently arose, she had gotten reports that the Crystal Empire would be returning. She would have to act fast in sending Princess Cadence, especially since she was getting reports of a new kingdom that has been annexing the lands South of Equestria.
Twilight herself had exited the airship that had landed in the snow outside of the Crystal Empire. It was freezing cold and she had no time to dwell before she felt herself attacked by some strange shadow like pony.
"King Sombra!" Twilight stated standing tall and facing the shadow pony but then an orb was thrown at him encasing him in stone. She turned around and saw Tempest smiling at her.
The Obsidian Orb was a weapon that had been discovered by the Storm King long ago and that he had adapted into his military's arsenal. It had used a magical repellent smoke that could be used to prettify any creature it comes into contact with as a statue. legend had it that it was invented by primitive Earth Pony mages on the orders of Chancellor Puddinghead.
Apparently it was to be used as a weapon against the Unicorns and Pegasi but the use and creation was shelved so they could focus on their food shortage.
"Don't thank me yet your highness, seems that due to King Sombra's nature as a shadow pony the Obsidian Orbs only work temporarily on him before he breaks free. That was the fifth Orb I had to use on him." Tempest explained as they were coming to the entrance of the Kingdom.
"As long as you are alright Tempest but please call me Twilight unless you want me to refer to you by your other name." Twilight told her with a smile which made Tempest step back with a nod.
"The legends said that the Crystal Ponies had their own artefact like Queen Novo has her pearl. They called it the Crystal Heart and Sombra took it when he took over so they could not use it against him." Tempest explained. Twilight then ordered the guard to be on standby with a deadlock preventing anyone else from entering. She said she would handle searching for the Heart while the others would focus on making sure the Crystal Ponies were okay.
"...make sure the Crystal Ponies are well fed and healthy, plus keep it a secret for now that Sombra is trying to get in. We don't want to worry them any further after all they had been through." Twilight ordered and Tempest gave a salute. Twilight went through the entrance as a carriage was flying through the distance of the sky..