The team investigates the murder of Jason Gideon.
Gideon had been investigating one of his and Rossi's original cases from forty years ago.
The unsub had shot him once through his window and then he had come into Gideon's cabin to shoot him two more times.
A man is in a wheelchair, apparently struggling to make a phone call at a phone booth but the phone isn't taking his quarters. An unsuspecting woman offers help. He tells her he's trying to get his sick dog to the vet, but his van has broken down.
She looks over and sees a big dog laying on the floor of the open van. She offers the man her cell phone and he invites her to go pet the dog. She does so. The man comes up behind her, gets out of the wheelchair, knocks her unconscious and abducts her in the van.
In a flashback, Rossi remembers he and Gideon discussing a series of murders that had taken place in Roanake, about an hour away from Gideon's cabin. At that time three women had been strangled to death, each three months apart. In each case, the killer had left each of the women dead in an open grave with a dead bird in her hand.
The team learns that another woman - this one much older - has been left dead in an open grave. Only she doesn't have a bird in her hand.
Rossi also remembers that another woman - named Tara - had gone missing. As the police didn't suspect foul play, he and Gideon could not investigate her disappearance. They quickly realize the latest woman found dead was the missing girl from that case.
The BAU believes that Tara was the fourth victim. Only she wasn't killed - they believe the unsub had kept her captive for all those years. They surmised that she had recently died, which is what set the unsub back out, looking for a replacement for her.
The medical examiner tells them that Tara had died of cancer, but that she had had injuries consistent with having her legs dislocated multiple times.
The BAU realizes that from the position in which they found Tara's body the unsub has a bird fixation. She hadn't been left in an open grave so much as a nest.
The abducted woman tries to escape from the unsub's apartment, only to be dragged back. He tries to feed her worms.
They receive word of her abduction and learn that she is a 23 year old woman named Josie Behdart.
The team finds out that the species of bird found on each of the victims those years ago is called a Nelson's Sparrow. It's a bird that's secretive by nature, and it doesn't listen to its own instinct to flee when in danger. Instead of flying away, it scurries away by foot. The unsub is choosing victims that match this type behavior: the victim has low self esteem and prefers not to make a scene, which is why they don't fight back or attempt to immediately escape when in danger.
By examining the local bird watching groups, Garcia determines that the unsub is a man named Donnie Mallick.
They realized that Mallick had killed Gideon because he had gotten too close to finding him.
Mallick finds and captures a Nelson's Sparrow. He brings the bird in front of Josie and kills it.
He dumps Josie out of a wheelchair and dislocates one of her legs. Later, right after dislocating the other one he hears the BAU arrive at his house.
He turns the light off and gags Josie.
He attempts to escape while holding his gun but Rossi has him dead to rights and he stops him.
Mallick places his gun on a barrel and raises his hands, while gloating about killing Gideon.
Rossi tells him that he'll be a big deal in prison for killing a federal agent, but a legend if he kills two.
Rossi puts his gun down, tempting Mallick to pick up his gun and shoot him. A shot rings out.
When the BAU rush upstairs and outside to find out what happened, they find Rossi standing over Mallick's dead body, with a gun in his hand.
In another flashback, Rossi remembers that it was this case that was the impetus for Gideon and Rossi to enlarge the team and create the BAU.
At that time, young Gideon and Rossi profiled each other to learn that they both were about to become fathers.
Gideon asks Rossi what his middle name is. He tells him it's Stephen.
Stephen is the name of Gideon's son.