Final Destination 21 takes place before the Final Destination series, what if all your life, when you were a little kid, you never remember anything what happened in your childhood, that's what happen to Sam and Katie when they were children, along with their older sister, Claire, and their cousin, Emily. Two siblings are about to get their own premonition from their father.
The film starts in 1998 where Sam (Nicholas D'Agosto) and Claire (Sophia Bush) help Emily (Audrina Patridge) pack her stuff in her new house. Sam found some videos from his, Emily, Claire and Katie (Emma Roberts)'s childhood, but couldn't remember what even happened. In 2000, after Kimberly and Thomas defeated Death and Brian's death, Katie, Erica (Shanica Knowles), Jane (Taylor Momsen) and Jared (Daniel Radcliffe) went to Bludworth (Tony Todd)'s warehouse. They video record and been caught, but Bludworth releases them and asks Katie if he remembers him. Katie, confussed, told him that she never met him, but heard of him before and leaves, making Katie a little bit worried.
- Will Forte as Richard Lawton
- Katherine McPhee as Lily Lawton
- Jake Short as Sam Lawton
- Nicholas D'Agosto as Adult Sam Lawton
- Jessica Tyler Brown as Katie Lawton
- Emma Roberts as Teenager Katie Lawton
- Kathy Hugh as Claire Lawton
- Sophia Bush as Adult Claire Lawton
- Caitlin Carmichael as Emily Lawton
- Audrina Patridge as Adult Emily Lawton
- TBA as John Wenser
- TBA as Nina Thomas
- Tony Todd as William "Will" Bludworth/When Katie was 6, she became friends with William, now she doesn't remember anything what happen. Sam, Claire and Emily all think that Will isn't real, but Katie think he is.
- Willow Smith as Erica Reese
- Shanica Knowles as Teenager Erica Reese
- Taylor Momsen as Teenager Jane McDonald
- Cameron Boyce as Jared Cooper
- Daniel Radcliffe as Teenager Jared Cooper
Richard, Lily, Sam, Katie, Claire, Emily,