The Marvel Cinematic Universe continues to expand and with that, the Marvel heads are making sure that each movie or TV show expansion is interconnected with the others. This idea of crossovers is something that always keeps the fans on their toes, which is ultimately great for the studio. 

Marvel is timing things perfectly as well. The latest report about an upcoming crossover comes from Screen Rant, where it is said that episode 19 of "Agents of S.H.I.E.L.D." titled "The Dirty Half Dozen" will be tied to the upcoming film "Avengers: Age of Ultron."  And the connection between the episode and the film will come in the form of Scarlet Witch and Quicksilver — or their background, at least. 

The twins were first revealed in the post-credits scene of "Captain America: The Winter Soldier." In that scene, the two superheroes were locked up inside a glass room where their powers were exhibited. A character called Dr. List was with them at the time. 

In "Avengers: Age of Ultron," no backstory is shared, only news that the twins will be joining The Avengers to fight against Ultron. But since Marvel announced the news, it shows that the company had plans of unveiling the backstory of Scarlet Witch and Quicksilver all along.

The official description of "The Dirty Half Dozen" goes:

Gonzales and Coulson must find a way to put their differences aside and work together against HYDRA, even if it means teaming up with someone they don't trust." 

According to Screen Rant, Dr. List may be the person Coulson and Gonzales will have to work with. The site also speculates Dr. List's involvement will be about the experimentation on the twins. 

"Agents of S.H.I.E.L.D." will air its next episode "Melinda" on April 14. "The Dirty Half Dozen" will air on April 28, prior to the screening of "Avengers: Age of Ultron" on May 1.