Warning: The following article contains spoilers for Luther: The Fallen Sun on Netflix.

A dangerous criminal is on the loose in Luther: The Fallen Sun — ironically, the only detective who can stop him is locked away in a jail cell. Not the most convenient circumstances when a killer sends a detective to jail!

Who is the voice taunting John Luther (Idris Elba) in prison with these ominous words? The voice tells Luther via radio, "And now you are in a cage, because I put you there."

So, what did Luther go to jail for in Luther: The Fallen? Read on for the dramatic details!

What did Luther actually go to jail for in 'Luther: The Fallen Sun'? (SPOILERS)

Unfortunately for Luther, all the laws he technically broke during the events of the original Luther series finally caught up with him. Crime doesn't pay, even for detectives who break the law for a reason! But how was Luther caught in the first place?

Naturally Luther's whole jail living situation doesn't suit him when he's taunted by that chilling voice on the radio. He needs to break the law one more time to put an old foe in jail instead, once and for all.

So, who is the voice on the radio that taunts Luther? It's none other than the serial killer David Robey (Andy Serkis). It turns out David was the one ultimately responsible for sending Luther to prison. After Luther is assigned to the case of one of David's victims, the serial killer reacts by digging up dirt on Luther and all the various illegal acts he committed chasing criminals.

As a result, David gets Luther fired and sent to jail.

Does Luther ever get released from jail? (SPOILERS)

Luther manages to escape in a dramatic jail break, complete with a fiery mattress, some help from an old criminal associate (Vincent Regan returning as Dennis McCabe), and plenty of punches.

Naturally, the next question to ask is if Luther gets sent back to prison at any point in Luther: The Fallen Sun. And does he ever catch David before he strikes again?

Thankfully, all is well that ends well for Luther at the end of Luther: The Fallen Sun. After a near-fatal confrontation with David (who ultimately meets his end in a frozen lake), Luther is approached by an official from MI5, who tells him he did a fine job dealing with David.

The mysterious MI5 man tells Luther that his chief would like a word with him and the door to a fancy black car opens with new opportunities for the crime-solving detective.

In other words, it looks like Luther redeemed himself enough not be sent back to prison. If you want to stream the original Luther series before streaming Luther: The Fallen Sun, you can watch all five seasons on Hulu.

Luther: The Fallen Sun is now available to stream on Netflix.