A common theory going around (which is what I thought as well) is that Scar Akai on earlier appearances was Bourbon (Amuro?), but this time it's Vermouth. Since it's most likely a disguise in the first place, more than one person could be using it at different times.
Also, we've seen in the past that Scar Akai apparently couldn't imitate Akai's voice, thus pretending to be mute when Jodie tried talking to him. However, this one can imitate Akai's voice convincingly enough to fool Sera (apparently finally confirmed to really be Akai's sister now). This implies quite strongly that this Scar Akai isn't the same person. We know Vermouth can imitate other people's voices very well. She also confronted Akai in the US about a year ago in-story time, so she could have gathered knowledge of Akai's family members like Sera, who was living in the US at the time.
edited 10th Jun '12 3:44:51 AM by riidenlieko
The mystery lady who was in Okiya's room and passed Scar Akai in a corridor is currently mostly theorized to be Yukiko. Other quesses (mostly before chapter 821, where we got more panels with her) include Fusae Campbell, Kir and Jodie. In any case, a master of disguise like Vermouth could most likely manage something more disguising than that. Also, the mystery woman and Vermouth have different-looking smartphones. Vermouth's phone was seen at the beginning of chapter 818.
Generally, a sum-up of theories about what's been going on: Bourbon (Amuro?) has been doing the Scar Akai act in front of Akai's colleagues to see how they react, so that he could figure out if the FBI people have some knowledge regarding Akai's possible fake death. The Scar Akai on the train is Vermouth, though.
Okiya is probably Akai in a disguise. There has been some unexplained stuff going on in the few most recent cases regarding his handedness, though... Akai/Okiya is left-handed, but recently he's been using his right hand a lot. Not sure why; there were theories that someone else is impersonating Okiya recently, but for now I'm going to assume Okiya has probably been the same the whole time. It's also rather obvious that Conan has known about the Okiya = Akai thing since the beginning, because Akai needed Conan's help to fake his death (the fingerprints on the phone). This sum-up based mostly on Chekhov McGuffin's theories - http://forums.dctp.ws/index.php?topic=3518.0
If Okiya's the same person as before, then the Mystery Lady with him should be one of the good guys as well. Okiya noted that the Heaven seems to be on their side, because when Ran, Sonoko and the Detective Boys walked into Amuro (Bourbon?), Haibara happened to be hidden behing everyone else, and thus Amuro didn't notice her. If Amuro has a "Black Organization aura", Haibara couldn't sense it because Vermouth's stronger aura covered it. Scar Akai definitely noticed Haibara, and after that, Gin was informed by Vermouth that Sherry is confirmed to be on the train. The Mystery Lady, on the other hand, couldn't have seen Haibara from where she was sitting.
Vermouth wants Bourbon to do the dirty job and kill Sherry, because Vermouth promised to Conan that she wouldn't do it. However, if Bourbon found out about Sherry's de-aging, then the rest of the Organization would most likely find out as well, which would mean danger to Conan. Therefore, Vermouth is probably trying to intimidate Haibara into taking the antidote; if she died in her adult form, the Organization wouldn't find out about the de-aging. Haibara seems to have figured out the same thing; she's planning to take the antidote and pretend to be uninvolved with Agasa, the kids, Ran etc.
edited 10th Jun '12 10:33:20 AM by riidenlieko
... Please tell me I'm not hallucinating.
◊ Did Conan actually say that to her?
OK, judging by the kids and Haibara's reaction
◊, he apparently did. Context, please?
edited 14th Jun '12 2:16:56 PM by MarqFJA
Fiat iustitia, et pereat mundus.Haibara and Ayumi were in an outdoor bath and found a dead body. Conan ran in a little...too quickly, and Haibara was ticked with him for the rest of arc.
She plants cayenne pepper in his pants afterward and arranges for her and Ayumi to be around when Conan needs to get the irritation looked at.
Author of The Second Coming (NGE) and The Coin (Haruhi).... <Face Palm> Did he have a death wish?! Man, for a Teen Genius, he can be so tactlessly stupid at time.
BTW, was that before or after this
◊?
That panel is basically right after Conan walked in on Ayumi and Haibara. The screencap is later on, as he's solving the case.
Author of The Second Coming (NGE) and The Coin (Haruhi).File 822 spoilers: Mysterious hat lady seems to be Yukiko. (AGAIN! Mysterious hat ladies are always Yukiko...) Scar Akai is Vermouth (this time; it can't have been her in the Red Shirts case). And yes, that is Vermouth, don't be fooled by the Akai wig that makes her look kind of like Kir due to Aoyama's art suffering from a case of Only Six Faces... Look at the blonde eyebrows. Also they have differently drawn eyes and eyelashes.
I think Okiya being a teammate of Yukiko confirms him as one of the good guys even more solidly than former evidence. Also, Sera getting stun-gunned by Vermouth after her shock of seeing "Shuu-nii" alive implies pretty strongly that she's not Bourbon, since Bourbon is working together with Vermouth. Also, Bourbon is supposed to hate Akai. Therefore, by process of elimination, yeah Amuro is probably Bourbon.
edited 15th Jun '12 12:20:39 PM by riidenlieko
@riidenlieko
If you ask me I think Bourbon is Amuro who is Scar Akai. The fact that Vermouth would use his identity to garner information proves this fact. Especially since Scar Akai's non-talkitive demeanor indicates the same thing. In addition if Okiya Subaru definitely can be taken off the list as being Bourbon considering he knows Conan's identity. If he did Conan would be dead in a heartbeat.
"I don't give a rat's ass about going to hell. I guess it's because I feel like I'm already there." -MugenSo I want to start reading the current arc...
Where do I start?
Improving as an author, one video at a time.

OMG 808 is so funny and awesome at same time
Sato kiss takagi but dont realise the Camera still running. so people in police HQ watching it
and oh sato is so badass
by the way did anybody read sonoci 4 Koma. they all pretty funny
http://forum.dctp.ws/index.php?topic=6145.msg489502#msg489502
for example
http://forum.dctp.ws/index.php?topic=6145.msg628947#msg628947
edited 21st Feb '12 12:22:17 PM by rrw