The six-part series followed flight attendant and single mum Jo Conran. Her life was turned upside down when she was blackmailed into drug smuggling for a criminal gang. The events began after her beloved son was imprisoned in Bulgaria for a murder he swore he did not commit.

So was the son guilty of killing a young boy in a bar fight in Sofia? What were the gang's motives, and how did Jo free herself from her predicament? Here's everything you need to know about the ending of Channel 4 thriller In Flight, starring Katherine Kelly.

***Warning: spoilers from the ending of In Flight on Channel 4 ahead***

[caption id="attachment_5958" align="alignnone" width="1500"] Katherine Kelly led the cast of gripping thriller In Flight, playing single mum and flight attendant Jo Conran [Credit: Channel 4][/caption]

In Flight ending explained on Channel 4: What happened in final episode?

Did Sonny kill the young boy in Bulgaria?

In the very first episode of In Flight on C4, Jo received a call no mother should ever have to receive. Her only son had been arrested in Sofia, Bulgaria, and faced a length jail sentence - 15 years to be precise. The crime? Murder. Sonny had allegedly killed a young boy called Kristian in a bar fight.

And this wasn't just any teenager. This was Kristian Georgiev, the son of an infamous crime boss. So did Sonny really do it?

The 19 year old told his mum: "This is a mistake. I didn't do it. Those lads in the fight, I didn't even know them."

As the series went on, we learnt that Sonny had been in a bar when a fight broke out at a stag party and spilled out into the street. He told his mum he'd then run away. However, three minutes later he was found standing over the boy's beaten body. Sonny insisted he'd been trying to help by calling an ambulance.

There were several minutes unaccounted for, when another fight broke out. This was the fight which resulted in Kristian's death. Remind us never to visit this particular bar in Sofia - sounds a bit feisty for our tastes.

In episode 4, a judge sentenced Sonny to 15 years without parole. He could serve his sentence in a British prison IF a fine of £300,000 was paid. A witness who believed Sonny was innocent suddenly changed his mind during the trial... Clearly this was a set-up.

Sonny was innocent. More on that below.

[caption id="attachment_6228" align="alignnone" width="1500"] Harry Cadby as Sonny Conran in In Flight [Credit: Channel 4][/caption]

What did the flashbacks mean?

During In Flight, Jo repeatedly had flashbacks to when her son Sonny was younger - probably around seven or eight. He was playing 'keepie uppie' with a football in front of goalposts in his childhood garden. At first it seemed like a happy memory that Jo kept reflecting on. However, the 'happy scene' changed into something more sinister when she remembered the moment to completion.

In fact, Sonny had turned angry and shouted at his mum to turn the camera off and stop filming in. He appeared to launch himself at her...

Was this simply a childhood tantrum? Or proof that Sonny actually had the sort of temper that might lead him to kill a man...?

Who was Cormac Kelleher?

So who was Cormac? Where was he from, and how did he end up working for the criminal organisation? He certainly seemed to be working on his own in the UK.

Jo described him as "cautious", never talking about his private life, or mentioning his bosses my name. In episode 3, an unhappy past was hinted at when we saw him watching his own father's funeral from afar.

Talking to Jo about her new life as a reluctant drug mule, he said: "This is your life now. Make peace with it. It's the easiest way." The man almost sounded sympathetic. Had he also been blackmailed into working with the gang? Or was he really the boss, and working alone? Was there even a criminal empire at all?

When former cop Dom used his police connections to look into Cormac, we discovered he had no previous criminal record - not even a parking fine. But that didn't mean he hadn't broken the law. We later learnt he'd started dealing drugs as a teenager. When the police caught him, he turned informer to stay out of jail. When some 'scary people' found out, Cormac ran. He left Belfast when he was 18, and travelled to Thailand. Once there, he "persuaded hippie kids to run drugs to Europe".

And that's how he met Aoife, who was 'one of those kids", and he fell in love with her.

[caption id="attachment_6229" align="alignnone" width="1500"] Scottish actor Stuart Martin as the mysterious Cormac Kelleher [Credit: Channel 4][/caption]

The truth about Aoife Ward, and which side Cormac was really on

We later discovered that Cormac was blackmailing several women - all of whom had relatives in jail. It became increasingly clear that Cormac was actually trying to help Jo. In episode 4, after Sonny had been sentenced, he warned her: "You've got to run Jo. Fifteen years is too long. He's never going to let you go."

As the final episodes progressed, we learnt that Cormac Kelleher was visiting a woman in prison by the name of Aoife Ward. She, too, had been smuggling drugs. Like Sonny, she received a 15 year sentence for smuggling heroin from Bangkok to London. She had an accomplice, but she refused to name them - so the judge came down hard.

Cormac told Jo: "Aoife wanted to take a risk. Set us up for life." But it went wrong, and she ended up in jail.

The pieces of the puzzle began to fit into place. Cormac was being blackmailed himself, just like Jo... Admitting everything to Jo, he said: "I'm being blackmailed, just like you. And I got a promotion from smuggler to middle man, but they still own me."

At this point, we were beginning to think the series could be similar to Code of Silence, where Liam did the wrong things for the right reasons...

With Aoife out any minute, it was clear Cormac planned to "cut and run". He knew too much, and Anton would want him dead once Aoife was out.

But Jo was prepared to do some blackmailing of her own to get the £300,000 she needed to get Sonny moved to a UK prison.

Who was Anton Marquis, the man behind the blackmail?

Cormac didn't give much away about his 'bosses'. However, he made it clear they were "evil people". The organisation that Cormac worked for had people inside the Sofia jail who were able to harm Sonny if Jo didn't do as they said - namely smuggle drugs.

If she did what she was told, Sonny would be protected.

In a rather shocking twist in the penultimate episode, Cormac told Jo they were both working for the police... That's when we learnt about Anton Marquis (played by Katherine Kelly's real life boyfriend Tony Pitts). He was "top brass" at the police, and therefore "untouchable".

Of course, Anton could have Sonny killed in an English prison, meaning Jo was "still trapped".

[caption id="attachment_6230" align="alignnone" width="1500"] Tony Pitts, Katherine Kelly's real life boyfriend, played bent copper Anton Marquis [Credit: Channel 4][/caption]

What was Jo and Cormac's plan to escape Anton?

Cormac and Jo made a deal to work together. However, he warned her she'd have to be "prepared to leave it all behind" - including her home, friends, and job. In fact, everything apart from Sonny.

Their plan? To smuggle more drugs than ever. Give the usual amount to the 'boss' and split the rest of the profits between them. That was all rather complicated by the fact that the pair appeared to be falling for each other, and ended up in bed in the penultimate episode.

The final episode began, and Jo prepared for what she hoped would be her final ever job for the organisation. However, Cormac's motives were unclear. Anton had promised him his freedom after Jo completed one more job. Cormac in turn told his boss that he'd tip off security so Jo would be caught.

That meant Jo would get the death penalty. When Cormac got up to make the call, Anton told him to sit down... He'd make the call. If Cormac had a plan, Anton had snatched it from his grasp. Had Cormac been beaten at his own game?

Was Jo caught smuggling drugs?

In sweaty-armpit-scenes, Thai police searched Jo's bag. But to her apparent surprise, her suitcases had no drugs in them. How and why, we would find out later.

The penny started to drop deliciously seconds later, when Anton himself travelled through security. Although we didn't actually see the moment Anton was busted with the switched heroin, the scene cut to Cormac and Jo the night before the flight from Bangkok to London...

Cormac handed Jo two bank cards to start a new life - all that was left after paying the £300,000 to bring Sonny to a UK jail. He also gave her a master key to the room 113, where the CCTV had been disabled.

That was Anton's room. Jo planted heroin in his suitcase. The next scene cut to Anton in a Thai jail, most probably facing the death penalty. We saw him make a call, saying: "You were right about the Irish man, no mercy now. Now get me the [bleep] out of here, and put in a call to Belfast."

[caption id="attachment_6234" align="alignnone" width="1500"] Cormac Kelleher was shot in the closing minutes of In Flight [Credit: Channel 4][/caption]

Did Sonny get out of jail?

In episode 6 of In Flight, Sonny was told his fine had been paid and he was moving to a UK prison. However, Sonny's police escort was intercepted by masked men wielding guns, and the British teenager went missing during the transfer.

News reports in the UK declared "British prisoner missing in Bulgaria". But was this Anton's plan to "tie up his loose ends", or Kristian Georgiev's crime family? Nope, it was little old Jo - with Cormac's help.

As the final episode continued, Jo met up with Kristian's mother, who seemed to have no idea where Sonny was either. She threatened to call the police, but Jo explained that the authorities believed the Georgiev had kidnapped him. It was a logical conclusion. After all, the crime family had taken a contract out on his life, which led to him being stabbed and almost dying.

Jo had proof of who really killed Kristian. Remember when she held a gun to one of the lads in the bar? Rory Rayson blabbed in fear. While Rory had had the first fight with Kristian during the stag party, a second fight later broke out. That time, Glen Lunt hit Kristian from behind and then he ran away. Jo gave Kristian's mum all the info she needed on the condition she left Sonny alone.

Jo and Sonny were subsequently reunited, and she told him what their future looked like. With new identities and passports, they would travel far away to run a bar on a white sanded beach off the beaten track in Thailand.

What happened to Jo Conran and Cormac at the end?

While Jo and Sonny made their plans to start a new life, Cormac - unbeknownst to him - was about to be ambushed at his house. Whether it was by Anton's people, or his former enemies in Belfast, we didn't know. Frankly, he had a lot of enemies at this point.

Snooping Dom, who had been staking out Cormac's place in hope of finding out what happened to Jo, witnessed it all play out.

The masked men shot Cormac in the stomach, leaving him for dead. But not before he managed to kill both of them, too. Dom subsequently did the right thing - well, of course he did, he was a nice guy! He dragged Cormac to his car, took him to the hospital, and even waited by his bedside until he woke up.

Of course, Dom just wanted to know where Jo was. But would Cormac tell him? Nope, not in this series anyway.

Meanwhile, Jo and Sonny made it to Thailand where they enjoyed their new life, alongside Kayla and the baby. But would Jo miss the rush? And would Cormac ever join them? The last words she said to him were "you know where I'll be".

[caption id="attachment_6235" align="alignnone" width="1500"] Ashley Thomas' character Dominic Delaney tried to help Jo, but was in over his head [Credit: Channel 4][/caption]

In Flight ending explained on Channel 4: What else happened in final episode?

• Aoife was free from jail, and set up for life. Cormac had done right by her. He'd set up three bank accounts in her name - with enough money to go away and start again. Which she did. She left Cormac with a forwarding email address. But he tore it up.
• Dom was back with Mel and his kids. Even though deep down he was in love with Jo, and desperate to know where she was.

Will there be a series 2 of In Flight on Channel 4?

Channel 4 has not confirmed a series 2 of In Flight yet. But we're expecting the series to be renewed. Although the ending of series 1 came to a satisfactory conclusion, with Jo and Sonny safe, there were plenty of loose ends.

Would Jo "miss the rush" as Cormac suspected? And would Cormac follow her to Thailand? And did Anton manage to escape the death penalty in Thailand?

In Flight was a great story, with characters we'd started to care about. Not least the growing relationship between Jo and Cormac.

We'd certainly watch another series, wouldn't you?

Read more: Inside the new Bella Ramsey thriller Maya written by Daisy Haggard and coming soon to Channel 4

In Flight is currently available to watch as a boxset on Channel4.com.