Sam drops Ruby off at school. One of her classmates starts to seize. 

Morgan Edge is on TV from a hospital full of children with lead poisoning. He blames it on the lead bomb Lena built. 

Maggie and Alex break up over their disagreement on kids. 

James thinks Lena should step down from CatCo. She puts James in charge until this is resolved. 

Lena holds a press conference and admits she doesn't know if her device is responsible. Someone starts shooting and James is hit in the shoulder. 

Winn does a test and determines there is a 10% chance Lena's device is the cause. 

Lena hides out at Sam's place for the night. 

Alex and Maggie share one last night together. 

Sam and Kara work together to try to figure out how the kids are connected. All the kids went to the same food truck near a public pool. Kara tests the water and discovers someone put a dangerous chemical compound in the pool. Kara calls Lena to let her know it wasn't her bomb. 

Lena confronts Morgan and accuses him of poisoning the pool. She pulls a gun on him, but is knocked out by another man. She wakes up on a plane. 

The DEO gets a distress call from Lena and Supergirl goes to her rescue. Morgan tries to remotely crash the plane, which would contaminate the water, but Kara fights to keep it in the air. The plane splits in half with the chemicals on one side and Lena on the other. Kara can't hold both halves and tells Lena to climb up and take her hand. 

Supergirl confronts Morgan who pinned everything on a patsy. 

Maggie and Alex share a tearful goodbye, and then Maggie leaves. 

LCorp gives the sick kids an antidote. 

Sam realizes that she was shot at the pep rally, but wasn't injured.