Ripper: Letter from Hell is about a woman, Molly Keller who survives being attacked by a serial killer. A few years after, she is in a forensic psychology class from an expert. While class is in session the instructor pretends to murder one of the students to illustrate that anyone has the potential for being a murderer. One of the students reveals that he knows about her past which makes her upset. He tries to woo her although she brushes him off. They all meet for a study session that night, but it ends badly. To blow off some steam the group leaves for a party where one of the students is murdered.
The detective that Molly knows shows up and informs her that he thinks that the same killer that tried to attack her is now back. One by one, students from Molly's class start to die. Molly shows her classmate, Marshall, that the pattern of the killings matches the same pattern as Jack the Ripper. Another classmate, Jason, convinces the remaining students that they should continue investigating despite what has happened. The group finds out about Molly's past. She leaves feeling upset when she runs into Marshall who comforts her.
The rest of the group continues investigating the theory of the murders being copycats of Jack the Rippers and realize that the victims all share the same initials as the original victims of Jack the Ripper. The group tries to call the detective although the phone lines are down. Molly becomes suspicious of both remaining survivors and knocks Jason unconscious when he gets back to the cabin. The detective finally arrives and knocks out the professor. Molly has a flashback of two men arguing back and forth. This leads her to consider that she is the actual killer. The movie ends without giving a clear view of who the murderer was, leaving it up to the audience to decide.