13 Reason Why Season 1

In season one, seventeen-year-old Clay Jensen returns home from school one day to find a mysterious box on his porch
Inside he discovers seven cassette tapes recorded by Hannah Baker, his deceased classmate and unrequited love, who killed herself two weeks earlier

On the tapes, Hannah unfolds an intensely emotional audio diary, detailing why she decided to end her life
It appears each person who receives this package of old-style tapes is fundamentally related to why she killed herself

Clay is not the first to receive the tapes, but there is implied detail as to how he should pass the tapes on after hearing them
There appears to be an order to distribution of the tapes, with an additional copy held by an overseer should the plan go awry

Each tape recording refers to a different person involved in Hannah's life contributing to a reason for her suicide
The tapes refer to both friends and enemies