Many public and university libraries have language learning sections. If your library doesn't own Fiesta Fatal, ask about interlibrary loan (ILL). They can borrow a copy from another library system for free.
If you are determined to master the content of Fiesta Fatal, here is a step-by-step study plan, regardless of whether you have a physical book or a legal e-book. Fiesta Fatal Pdf
Ask a classmate if you can take photos of the assigned pages. Most teachers allow this for a single homework assignment. Be responsible—don't photograph the entire book. Unlocking the Mystery of "Fiesta Fatal PDF": A