'I can't work out whether it's amazing, genius or the worst episode I've seen!': Sherlock fans go wild over 'gory' series finale ... as it causes a divide between 'confused' viewers

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The third and final episode of Sherlock's much anticipated and debated season 4 aired on Sunday night. 

And it proved to be the most explosive, mind-boggling one to date.

With Sherlock Holmes, Mycroft Holmes and John Watson finding themselves forced to solve an evil and violent crystal maze designed by their re-emerged evil sister Eurus, fans took to Twitter to voice their amazement at the season finale. 

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The ultimate mystery? The third and final episode of Sherlock's much anticipated and debated season 4 aired on Sunday night

Good or bad? Viewers weren't quite sure how to take the show and were hugely divided 

'I can't work out whether it's amazing, genius or the worst episode I've seen!' one confused viewer wrote. 

'I'm still in shock, I don't know how I'm supposed to sleep,' another tweeted, as one added: 'Does anyone actually understand Sherlock?'.

And confusion appeared to be the general consensus, with another writing, 'So, anyone fancy explaining that to me?', adding to the 3000 tweets sent in an hour. 

The season finale began with a little girl waking up to a plane-full of unconscious passengers, surrounded by hanging oxygen masks.  

Tense is an understatement: It proved to be the most explosive, mind-boggling one to date

The spooky scene saw the little girl wandering through the creaky and dimly lit plane, shouting 'help me', to a ringing phone.

'Hello, my name's Jim Moriarty', a voice answered as it cut to a creepy scene of Sherlock's brother Mycroft watching a black and white movie.

But his peace was disturbed by an eerie whisper as he followed an open door down a dark corridor and was greeted by life-sized doll of a little girl before following her up the stairs.

Confusion: The episode received mixed reviews as viewers voiced their shock

As he was ambushed by a menacing sword-wielding clown, Sherlock appeared, ending the set-up with a mere whistle.  

'Conclusion: We have a sister confined for years and you are terrified by her,' he exclaimed, as John Watson joined him.

'You wouldn't have admitted the truth if we hadn't have scared you witless,' John explained, as Mycroft looked on in shock. 

'I was protecting you, you couldn't remember her,' Mycroft protested, 'I was remarkable but she was a genius beyond human. She was different from the beginning and knew things she shouldn't have.'

'Never been so mind-blown': A Twitter storm ensued following the trippy episode

Flashing back to early memories he revealed, 'They found her cutting herself with a knife and she explained she wanted to see how her muscles worked.  

As Sherlock began to remember memories with the little girl, it emerged she had drowned their beloved family dog Redbeard, traumatising him as a little boy.

And Mycroft revealed Sherlock had blocked out memories of the girl after she set the house on fire and was taken away from the family.

'She started another fire which she did not survive', Mycroft explained.

'The depth of Eurus' psychosis was too much for normal people to understand, so that was the cover story anyway.'

'Where is our sister?' Sherlock shouted. 

Mystery at home: Sherlock and John realised he there was another Homes- sister Eurus

'I was trying to protect you', Mycroft admitted as he explained she was taken away as a girl

'She is in fact on an isolated secret island called Sherrinford, and that's where she's been since her childhood. Whoever you met it can't have been her,' he claimed.

But their conversation was interrupted by the sound of her singing East Wind as a grenade buzzed into the room.

'Don't move, it's motion detected and we'll all die', Mycroft warned. 

With seconds to spare they jumped out of the windows in a dramatic scene not far removed from one in Bond, as the mine exploded into enormous flames. 

Genius or psychopath- or both? Eurus Holmes had been kept on Sherrinford island since childhood

Back from the dead: She conspired with Moriarty, recording video messsages before his death

The scene cut to fisherman caught in a storm, before the words 'Sherinnford' flashed up on the radio waves. 

And the sailors were shocked to discover Sherlock and John were on the ship,  as they were forced at gunpoint to fake a collision with the island. 

As armed men dashed out, they found a fisherman tied to John up next to a message written in the sand, 'Tell my sister I'm here', it read.

With Sherlock nowhere to be found, John revealed the fisherman was in fact Mycroft in disguise.

Childhood home: The episode featured a flood of flashbacks to the Holmes' childhood home

'You should be looking at the man you just gave your pass to', they grinned at the baffled security guard, as Sherlock escaped into the lift.  

'Keep your distance', a passing guard warned as Sherlock headed to meet Eurus through armed wards and cordoned off tunnels.

Eventually he found her playing a violin, her back turned to him in a scene that echoed Margot Robbie's cell in Suicide Squad. 

'Eurus reprogrammes people. Anyone in contact with her is compromised', a doctor revealed.

'Mycroft told me you'd rewritten your memories but not that you'd written me out completely. You still don't know about Redbeard do you? This is going to be such a good day,' Euros whispered as she met Sherlock. 

'Tell my sister I'm here', The Homes brothers and John Watson broke into the ward

The scene cut back to John and Mycroft questioning the doctor before they realised he too had been 'enslaved'.

On the discovery the doctor called security, surrounding them, as the scene cut to Sherlock being attacked by a suddenly free Eurus.

And as she began choking him, she commanded the armed security to step back and watch as it emerged the whole prison was under her command. 

As chaos ensued, the scene threw back to the late Moriaty and Mycroft meeting in the dingy confines of the island five years prior to the date. 

Mycroft had given five unsupervised minutes of Moriaty's time to Eurus as a 'Christmas gift' after she correctly predicted three terrorist attacks.

In disguise: John Watson and Mycroft broke onto the island after taking over a sailor's ship

It soon emerged she had used the time to film short eerie video messages of Moriaty, as he would die months later.

Bringing the scene back to the current tense,  the trio were trapped along with the doctor, with Eurus running the prison.

In the background the doctor's wife was seen gagged and bound, struggling in the background.

'One of you has to kill her or each other', Eurus demanded, as the desperate trio debated who should shoot the struggling woman.

Violent and tense: Eurus introduced fear of murder with constant threats and time constraints

As John prepared to shoot the doctor to the pre-recorded sounds of Morioty whispering tick tock, the doctor grabbed the gun and killed himself.

'Because you don't want blood on  your hands Dr Watson, two people are dead', Eurus said, shooting the doctor's wife calmly.

'Sherlock pick up the gun, when I tell you to use it, do so,' she demanded next. There's only one bullet but you'll need it.'

Next Sherlock was commanded to solve a murder case, with three suspects dangling precariously in front of his window, suspended over the ocean. 

Despite him guessing the correct culprit, all three were plunged into the ocean, as it cut back to the girl on the plane calling for help.   

The little girl's voice re-emerged from the plane, as it appeared she was heading straight for a city in the errand plane. 

But her call for help was cruelly cut off as they were tasked with first calling Mollie Hooper and persuading her to declare her love for Sherlock.   

Resembling a Crystal Maze scene, they moved onto the next task. 

And in a shock twist, Sherlock pulled the gun on his brother, before changing his mind and turning the gun on himself.

As Eurus screamed 'Stop it!', he counted down as he held the gun to his neck.

But the scene was interrupted as the trio were sedated, with Sherlock waking up in a cell alone, and back on the phone with the little girl.

'You were gone for ages,' she complained, as he directed her to the front of the plane. 

Next John woke up in a water-filled dungeon, shouting to Sherlock: 'I'm chained to the bottom of the water and it's filled with small bones. 'I'm in the bottom of a well', he shouted.

As the little girl attempted to fly the plane, it started to plunge to the ground, as Sherlock broke down the wall and found himself in a childhood graveyard.

Mind games: Eurus set Sherlock a crystal maze of tasks, with an underlying threat of a dying little girl and potential death of John trapped in childhood well

'Find Redbeard or you won't save the little girl and I'll drown another one of your pets'.

Scenes intensified as the girl screamed that the plane was crashing, while John shouted that the well was filling up. 

As he tried to solve the mystery of Redbeard, John shouted: 'The bones I found weren't dog's bones.

'We never had a dog', Eurus interjected, 'that's what you told yourself as you were upset'.

And it flashed back to Sherlock playing with a little boy named Victor. 

'You were inseparable but I wanted to play too,' Euros cooed, as the scene cut to the little boy trapped in the well, with John discovering a skull in the filling well. 

'You killed my best friend,' Sherlock cried to Eurus, 'Redbeard was a little boy'.

Time constraints: Sherlock was tasked with solving mysteries in minutes, set by Euros, who murdered hapless victims in front of them

'I never had a best friend, I had no one,' Eurus hit back.

 With Sherlock figuring out the key to the whereabouts of the filling well, tense scenes showed John being submerged as the little girl continued to crash.

'It's time you told me your real name, I'm not a stranger- I'm your brother aren't I?' Sherlock said, as he found Eurus rocking alone in deserted attic, her mind casting her back to the lonely crashing plane.

'Open your eyes I'm here and you're not lost anymore,' Sherlock comforted her as she finally broke down.

'I was lonely': The trapped little girl on the plane turned out to be Euros, desperate for brotherly love

'Help me save John Watson.' 

The finale ended with Eurus being led away by police, as John dried off in a towel, his life saved by his best friend Sherlock.

And Paul Weller made a surprise cameo appearance at the end of the Sherlock finale thanks to pal Martin Freeman, appearing briefly as a fainted Viking in the last scene.

'When life gets too strange and frightening, there is one last hope. Two men arguing in a scruffy flat, like they always have been there and always will. 

'My Baker street boys Sherlock Holmes and Dr Watson', were the final words in a video message from Mary Watson, as the scene cut to Sherlock and John tidying the blown up flat as they moved back in with John's growing daughter Rosie, Sherlock's goddaughter, returning safely to their old routine.

Celeb spot: Singer Paul Weller made a surprise cameo appearance at the end of the Sherlock finale thanks to pal Martin Freeman

Happy end: With Euros safely locked up, the trio were back in the apartment, their friendship fixed