He's wearing a whale the size of a dog on his head. Her mask is a fly, with plate-sized compound eyes. They both stare at me for a moment, then the fly woman says:

"I don't know how you can wear that mask. Disgusting."

I'm at the only place a masked criminal can walk around in plain sight: a masquerade party, thrown by Lady Boyle in her lavish mansion. The ceilings hang with silver silk, confetti periodically pops from the chandeliers, and music floods the house. I'm here to kill her.

The trouble is, there are three Lady Boyles: sisters. I don't know which one is working with the conspirators who framed me, I don't know any of their first names, and I don't know what any of them are wearing tonight. All I've got to do is find all that out and kill the right one, with a few dozen guards and a house full of party guests watching me. I think I'll start by stealing this guy's wallet.

Dishonored feels like Thief: a dark, complex first-person stealth game loaded down with things to nab - some of which can be snatched right from the belts of dim-witted guards and corrupt socialites. Unless five party guests and two guards see you do it.

My death is strange and frightening, even for a death. While the regular guards come running, two men in golden masks step out from their posts by the walls and walk slowly towards me. Overseers. As they march, they wind mechanical music boxes around their necks to grind out a grim dirge. Their song seems to darken the world, and drains me of all my supernatural abilities. I'm impotently hammering my teleport spell when the others cut me down.

The duel

I restart, and decide to try talking to the guests. And suddenly it starts to feel like Hitman: the party is a public neutral zone that I'm free to roam, studying potential targets and figuring out who I can get alone. And like Hitman, the costume and environment design are exquisite.

Whale head and fly face are the tip of a grotesque iceberg: one woman has a sort of cheetah mask with glaring eyeballs. One man's red tribal mask has a screaming vertical mouth. Another woman is wearing a life size baby doll upside down on her head, its head twisted the right way up to cover her own.

As I walk around the party, I get chatting to a man wearing half a fox's head. It turns out I have a letter for him from one of my society friends. Not having played the preceding section, I am unaware that this letter challenges him to a duel. Er, okay!

In the back garden, we're handed our pistols and instructed to take ten paces away from each other. I start to get a little nervous. Three! This seems worryingly fair. Two! Isn't there someway I can be a douche about it? One!

I freeze time (I can freeze time). I'm slightly early, so I don't pull the trigger - I just line up an exact headshot and wait.

Time restarts. He turns. I fire. He drops.

The arbitrating guards chat distractedly about what to do with the body, and I breathe out and head back inside.

That's when I meet the scarecrow. His mask is just a sack, really, with two staring eyes and unexplained whiskers sticking out at every angle. The scarecrow talks to me. He says he knows what I'm here to do. To kill Esma Boyle. But he's in love with her. If I bring her to him in the basement, he promises they'll disappear without trace. It seems like a kinder option, until he mentions he wants her unconscious.

The woman in white

Still, now I have a name. I just need to match it to a costume. The sisters' bedrooms would be the best place for clues, but the main stairs are blocked by an energy field programmed to vapourise intruders. Even if I can de-power it, there are guards everywhere. So I'm not going to depower it. Instead, I follow the cables round to a side room. It's locked, but I spy the key on a guard's belt and carefully lift it. Inside, I use a rewire tool to switch the field to my side: it'll kill everyone but me. I'm not going through it just yet, but it's going to make things a lot easier if a fight breaks out.

There's also a rat in here. I can Possess the rat. I Possess the rat, and scamper into the building's vents. By the time I return to human form, I'm in the master bedroom.

Getting around upstairs is trickier - it costs a lot of mana to Possess things, so I rely on conventional sneaking and the much appreciated ability to peek around corners. From letters, clues and diaries, I discover that Esma is in white, and that she's planning to "bed the first man who asks - and the next." Since that would probably involve her walking through the forcefield at the bottom of the stairs, I plan to ask.

Her identity isn't a spoiler, by the way - it's randomised every time you play.

First I have to get down. I can't find any rats to Possess, so I sneak out onto a balcony - right in front of a guard. He tells me to get out, then walks back to his post. I'm grateful he didn't attack, but he's a liability - the moment his back is turned, I put him in a sleeper hold and toss him into the shadows. I hop onto the balcony rail, see an open window across the street, and teleport deftly inside.

I'm falling. It's pitch black. I hit the ground with a crunch, a whisker from death, and look up. Every floor in this building has collapsed from rot: it's just a timber-strewn husk. God damn it! I drink a health potion and stumble out into the courtyard, nodding to the same guards I passed on the way in.

The delivery

Back at the party, I find Esma. It only takes a few flirtatious dialogue options for her to invite me to her room, but she leads me in completely the wrong direction. Dammit! She's taking us up the servant's stairs to avoid attention. She waves me past the masked Overseer and up the steps. I put her in a chokehold until she passes out.

This is a tight spot. Upstairs is crawling with guards, and the stairwell we came through is in direct view of the whole party. But I'm very close to the basement scarecrow guy wanted me to bring her to, and I'm sort of morbidly curious to see how that works out.

I look back the way I came, and very carefully aim a teleport spell to the opposite side of the doorway looking out at the party. It's a perfect jump. Except that there are two guards on the stairs below, and now they're both looking up at the guy carrying an unconscious noble to the basement.

I teleport past them and sprint downstairs, bolting into the kitchen and ducking behind a stove, Esma still slumped over my shoulder. The guards come snooping, but not hard enough - eventually they amble off. A backpassage leads to water that runs under the house, and sure enough, scarecrow guy is waiting for me. I place Esma in his boat.

"You don't know how much this means to me," he says, looking at me with blank glass eyes. "I'm sure she'll come to appreciate me in time. After all, we have forever."

He continues to stare at me as his boat drifts slowly down stream.

Oh I have not done a good thing.

The kill zone

My route out is going to be tricky: the place is crawling with guards, and they know me now. But I still have that energy field on my side, so things will get a lot easier if I can reach the main stairs. I use the back stairs to get to the top floor, and sneak round from there.

I stand at the bottom of the main stairs for a while before the guards notice. The first one shouts and runs to the alarm bell. I watch patiently as he sets it off, then runs at me and dissolves into particles of white light. The Overseer glares at me, starts winding his music box, and marches slowly forwards. Two guards from upstairs hear the alarm and come running. The music has shut down all my powers, so I fight them on the stairs with my sword.

Dishonored's sword fighting is simple but decent: enemies are quick to slash, but if you block their blows at the right time, your counter attack is an instant kill. Big fights are sloppy, but with practice, one or two enemies can be handled quickly and neatly. My style is a little messier - I end up simply shooting one of them. I finish just in time to turn around and see the Overseer march right into the energy field.

He's atomised. The song stops. My powers return. Two more guards run down the stairs. I step to one side, take two steps up, turn, and cast Wind Blast, knocking them both over the bannisters. One is killed by the fall. The other tries to run back up the stairs, so I Wind Blast him directly into the field.

There's one more guard in the lobby, understandably wary about crossing through the field to get to me. I try shooting him with my crossbow, and there's a hiss as my bolt is incinerated by the field. Huh!

In combat, Dishonored almost feels like BioShock: you've got a wide array of weapons and magical powers, and you can upgrade them or buy new ones as you progress. Its complexity comes from how you combine them, and how they interact with the logic of the game world. Wind Blasting someone into a rewired death field works, but shooting through one doesn't: it sticks rigidly to its rule of killing anything that isn't you.

The escape

I step through the field and shoot the guard in the neck, then head out into the courtyard.

It's an awkward moment. I'm right next to the main door guard, and two more are patrolling the grounds ahead. No-one's seen me, so I can't tell if they're going to be hostile. But if I wait to find out, I won't have the jump on the guy at the door. I stab him in the neck to be safe. The other two guards hear it happen, so I cast Freeze Time and cut both their throats before they can react.

I'm not sure if this is coming across yet, but there are a lot of goddamn guards at this party. I hear more on their way and duck into an empty building. After four flights of stairs, I realise it's the wrong call. I can't see any way out, and at least four guards are running up after me.

I've used up my mana potions on all that Wind Blasting and Time Freezing, so I've only got one full bar left - I need to make it count. When the first guard comes barging in, I Possess him.

The other guards all stop, confused by my disappearance. As the possessed guard, I push my way silently past them, down the stairs, and back out into the courtyard. The spell wears off just as we leave, and when I step out of the guard, he staggers forward and throws up. I politely wait until he's finished, then run him through.

It's finally quiet, and I can find my way down to the waterfront.

"Hope you enjoyed your evening," my getaway boatman Sam comments casually.

I did. It was one of the best missions I've played in any game. It combined the sophisticated murder-planning I love in Hitman with the old-school stealth of Thief, and the unpredictable, systems-driven combat of BioShock. Going back and exploring all the paths I didn't take, the city blocks of explorable space I missed, gave me a taste of its extraordinary scope.

This was also my first time with the PC version, and it's so much nicer to play. When you're in precise control of this huge toolset of abilities, in such intricate open environments, it really starts to feel like something special.

Dishonored is out in October. The latest trailer for it is awesome. I wrote another diary like this about the mission before this one.