Grell Sutcliffe is first revealed as the Burnett Estate butler when Ciel Phantomhive and his butler, Sebastian Michaelis, move to the Phantomhive townhouse within London after receiving a letter from the Queen. Madam Red, otherwise known as Angelina Darres, comes to the townhouse to visit her nephew and brings her butler along with her. Ciel was called to London to investigate the strange murder of a young woman named Mary Ann Nichols in the Whitechapel area. The brutal way in which the woman was murdered and dissected led the London papers to nickname the murderer something truly gruesome - Jack the Ripper. Grell accompanies Ciel, Sebastian, Madam Red, and another of their acquaintances, Lau (a Chinese "businessman" with somewhat shady connections), as they begin looking for information regarding the murders. Grell plays a nearly inconsequential role throughout the investigation. He spends most of his time just trying to keep Madam Red's hotheadedness under control, or bringing her tea and running small errands.
After speaking to an underground informant known as the Undertaker, Ciel's group learns that the suspect must have medical knowledge. Ciel orders Sebastian to put together a list of people who could possibly be the Ripper and crosscheck their alibis and Sebastian takes off to do just that. And when I say "takes off," I mean he steps out of the speeding carriage that Grell is driving. At that moment, Grell seems to take a liking to Sebastian for his dedication to his job as Ciel's butler and his amazing abilities. On the other hand, Grell gets lost on the way back to the Phantomhive townhouse and it takes longer than expected to return. Once they arrive, however, they're greeted by Sebastian who has already finished gathering the suspect list and has even finished preparations for afternoon tea. Yet again, impressed by Sebastian's abilities, Grell swoons a little more for him in the background.
Sebastian has narrowed the suspects down to one person, the Viscount Druitt, Aleister Chenbar. Everyone goes undercover to investigate Aleister, and although he's caught and found guilty of holding illegal human auctions behind the scenes of his social galas, another murder is committed while he's in police custody. Annie Chapman dies by Jack the Ripper's hands and Ciel and Sebastian have to look over the list of suspects again. That night, as Ciel and Sebastian go over the paperwork and suspect list, Madam Red appears and asks Ciel to play chess with her in order to give him 'a break.' Grell appears as well and is told to make tea, but he's so terrible at it that Madam sends him out to redo it all.
While he's out, Ciel and Madam talk about the past and Ciel eventually wins the game and retires for the night. Grell returns just as he leaves and is witness to Madam Red asking Sebastian to stay by Ciel's side and protect him because he won't turn away from the path he's on, no matter how dirty and twisted it might become. Sebastian retires after his master and Grell looks to his mistress, only to see her get a strange look in her eyes as a storm rolls in. He seems taken aback by the coldness in her eyes, but before we can see what happens next, the scene cuts away to Ciel and Sebastian. Ciel realizes that Sebastian hasn't been telling him the entire truth in that Sebastian only collected a list of possible human suspects. With this new knowledge, they once again go out to see who Jack the Ripper really is.
To do this, they stake out Mary Kelley's home (the next assumed victim), standing guard at the only entrance to the alleyway to her home. Unfortunately, even though they're guarding the entrance, they hear a scream and rush to the room to find her freshly ripped apart inside. Ciel is the first on the scene, but Sebastian covers his eyes to shield him from the horror as he speaks to "Jack," who is still inside.
Grell Sutcliffe steps out, covered in blood.
He tries to say that he was just passing by, but since Ciel and Sebastian were guarding the only entranceway, Sebastian refuses this excuse. He then calls Grell out on what he really is - inhuman - and praises him on hiding himself so well as a butler.
Grell loves the praise and finally reveals himself, undoing the ribbon that holds his hair back, taking off his rounded glasses, and combs out the black hair dye in the falling rain from the storm to reveal blood red hair. He puts on fake eyelashes, dons a pair of black gloves and replaces the rounded glasses with a pair of red framed ones while he reintroduces himself as the Burnett Estate butler, Grell Sutcliffe. Grell expresses his surprise at seeing a demon acting as a butler, but Sebastian throws back that he's never seen the same with what Grell is: a death god, or shinigami. In the Kuroshitsuji world, death gods are like demi-gods, halfway between God and humans, so Sebastian says they are close to 'gods' in a sense. Sebastian asks why Grell has descended to Earth to commit these crimes and he replies that it must be because he's fallen in love with a 'certain woman.' That woman is, of course, Madam Red.
Ciel explains that since Grell is a death god and, therefore, not human, he and Madam Red are the only people capable of committing the crimes. Only Grell could have slipped past Sebastian and Ciel in a second, and only Grell could have gotten from the Viscount's home in the West End to the scene of the crime in the East end and back in a matter of minutes. No one would have noticed an attendant missing from a social gathering, giving Madam an alibi while Grell was off doing her dirty work. And the victims were all patients at Madam Red's hospital, where they underwent abortions by the Madam's hand. They also died in the order which they received treatment.
Caught by the truth, Madam admits to having killed them, but she refuses to give up and that's when Grell springs into action. He attacks Ciel with a red chainsaw - his deathscythe - and Sebastian is forced to intervene, starting a long battle between the two of them. While Sebastian and Grell are fighting, Ciel faces off against Madam and in a fit, she tries to stab him, only to find that she's unable to hurt her only nephew. Although she stops before actually stabbing him, Sebastian is tied by contract to protect Ciel so he ends up almost losing an arm to Grell in order to attack Madam. Ciel stops him though and while Madam cries about how she can't kill her nephew, Grell is left on his own, and he isn't happy. He asks why Madam won't kill Ciel when she's killed so many women before and when she still refuses to kill her nephew, he kills her by shoving his chainsaw through her chest.
Her life is revealed via Cinematic Record, the main power of all death gods in the Kuroshitsuji universe. Once cut by a deathscythe, the blood turns into film strips that play a person's life back before their eyes and the eyes of a death god, allowing them to decide whether to kill or let live, and whether to send a person to heaven or hell. Grell seems to really enjoy watching people's Cinematic Records, admitting that he does have a bit of a bad habit for peeping at people's pasts. He can't help himself because he likes seeing the dark secrets people hide.
We learn that the reason Madam started killing women was because she had a one-sided love with Ciel's father, who chose her sister over her. Madam eventually married and even conceived a child, but an accident with a carriage killed her husband and robbed her of her child and the ability to bear any other children. Ciel's parents are murdered after that and one day the Madam snaps after giving a prostitute an abortion. She decides that if the woman doesn't want the baby in her womb, then she doesn't deserve to have one and kills her the night after her surgery, ripping out her womb. Grell has apparently been watching Madam for awhile now and decides to help her because he says that they are "alike" in that he wants to have children, too, but because he's male, it's impossible. Together, they turn into the avenging angels of God, going after "ugly" women who destroy the gift that God has given them. Grell goes off the Death List, the predetermined list handed down from God naming those who are supposed to die, in order to help Madam Red with her objective of punishing unworthy women. He enjoys the death and the blood and so his desires line up with the Madam's own quite nicely. However, when Madam refuses to kill Ciel even though he would blow their cover, Grell kills her because he's upset that she would throw all their work away.
After stripping Madam Red of her coat and expressing his dismay at her having become an "ordinary woman" after all the rules he broke for her and all the trouble he went through to help her, he starts to leave. However, Ciel tells Sebastian to capture Jack the Ripper per the Queen's orders and the fight starts anew.
The fight itself showcases how fast and difficult Grell can be as an opponent, but it also shows how very, very weird he is. He spends most of the fight professing his love for Sebastian and the more Sebastian threatens him, the more excited Grell seems to get. He obviously enjoys the fight and takes great pleasure in teasing Sebastian about his infatuation with him, saying that he thinks he could have Sebastian's baby if they tried. Which…Sebastian does not appreciate. They fight until Grell gets a good swipe in at him, cutting Sebastian across the chest. Instead of getting a juicy bit of backstory, he gets a nasty introduction to the banality that Sebastian faces day to day at the Phantomhive manor. Pissed that he didn't get to see the dark details of Sebastian's life, they go at it again, only this time, Sebastian has a plan.
Using his torn jacket, he stops Grell's chainsaw and renders him incapable of fighting. Against a demon's strength, Grell loses easily and is beaten to a pulp. Sebastian then takes the chainsaw and attempts to behead Grell with his own weapon, when Grell's supervisor, William T. Spears, appears and "saves" him. After stopping the beheading though, William beats Grell for having gone against the rules and drags him off to file the appropriate paperwork for the situation. And thereafter, Grell has never been heard from again.