The Lisbon Sisters Timeline and Summary

Cecilia tries to kill herself by slitting her wrists in the bathtub.
The girls have a party for the neighborhood kids to give them an opportunity to socialize. (Their psychiatrist suggested it.)
Cecilia jumps out the window during the party and kills herself.
The remaining sisters attempt to return to normal life, and go to the homecoming dance on a group date with the narrators.
Lux is crowned homecoming queen and has sex with Trip on the football field. She comes home later than curfew.
The girls are grounded and even forbidden from going to school.
Lux is taken to the hospital for a burst appendix and asks for a pregnancy test and gynecological exam.
The sisters start sending messages to the neighborhood boys and talk with them once on the phone. They ask them to watch for their signal, supposedly to help them escape from their family.
On the indicated night, the girls all kill themselves in various ways. Lux distracts the boys while they do it. Mary survives her suicide attempt.
A month after returning home, Mary finally kills herself by overdosing on sleeping pills.