Nearly two years have passed since the Netflix serial-killer drama “Mindhunter” dropped, but Season 2, which arrives Friday, picks up as if no time passed. When last we left the F.B.I.’s nascent Behavioral Science Unit, it was 1977, and the unit was still fighting to persuade skeptics that interviewing serial killers was a worthwhile pursuit. And then things got dark, even for a show about serial killers.

Understatement alert: Interviewing mass murderers seems very stressful. So does working in a basement. Little surprise, then, that the unit was a mess by the end of Season 1, with Special Agent Holden Ford ( Jonathan Groff ) in a panic attack; Special Agent Bill Tench ( Holt McCallany ) in a rage; and a cloud of mistrust hanging over their teammates, Special Agent Gregg Smith ( Joe Tuttle ) and the psychologist Wendy Carr ( Anna Torv ).

When Season 2 opens, Holden is literally strapped to a hospital bed. What landed him there? And what was the deal with the audio tape? Here are some important details to keep in mind from Season 1.

1. Holden’s Collapse

Pride goeth before a fall. Holden barely had time to bask in the glory of solving the murder of a 12-year-old girl near Atlanta before his world came crashing down. His girlfriend broke up with him. His colleagues were annoyed at his cockiness and methods, which had garnered some problematic press coverage and were threatening to bring down the unit. Then a hospital called to inform him that the serial killer and necrophiliac Edmund Kemper ( Cameron Britton ) had tried to kill himself — and listed Holden as his medical proxy.