Sly Cooper is a game if you want to learn more about it watch the games cutscenes on YouTube.

Here is a Sly Cooper Story idea what if Sly was kidnapped by a mystery person who was ordered by an evil Princess who was in love with him but Sly was not in love her, because he as feeling for Carmelita Fox. So the Princess going to brainwash him to make him forget his past, will The Cooper Gang and Carmelita Fox save him ?

Here a another idea

What if the Contessa was trying hypnotize Sly instead Carmelita ? What if the Contessa wanted to make him forget Carmelita ? And Bentley actually freed Carmelita and she agreed to help him to only take down the Contessa and Neyla, but when she destroys the brainwashing machine it causes Sly to be unconscious, Carmelita got him out along with Murry. Who stop the Contessa and got the Clockwork eyes, later when they were in a safe place Sly woke up and when he see Carmelita he ask Bently who she is. Will Sly ever remember her and his feeling for Carmelita ?

Here is another idea

When Dr.M shot Sly, some mysterious people kidnap him when he was unconscious, before Carmelita could get to him. The mysterious people took Sly to a secret hidden location because a princess have been spying on him. (In the second Sly Cooper game Band of Thieves the ending since then) she was very interest in him and when she saw a picture of Sly she immediately want him here to be part of her little gang. So when Carmelita saw a small glimpse of Sly (Who is brainwash or have amnesia been believing lies that the princess and servants tells him) Will his friends and Carmelita save him ?

It's an AN one where before Thieves in time like another two or three years. Oh and the princess met her human counterpart and they both made each other a deal, so the princess and the gang secretly steal things from the human world and the human princess counterpart gives them cover or some of the things they steal given to her.

P.S. can be after Thieves in Time if you want.