I believe that the other scent that Natsu smell is it by Lucy.
In fact she was in the room at the beginning of the chapter.
And it is surely Lucy, because in fact she was not with the other at the announcement of the fight between Tobi and Kurohebi, in fact in the second frame of this page http://www.mangareader.net/fairy-tail/277/5 we can see clearly that she was running to reach them, to see the fight.
I believe this this because I don’t think that other people could enter in that room.
In fact the member of Raven Tail were watching the match between Kurohebi and Tobi, while the evil knight was with the king.
Beside that knight has not interesent in Wendy and Charle, at least for now, because he did not know that Charle can see the future and that she had a vision that can jeopardize the outcome of his plan.
Except for Raven Tail for the one that I said above I think that only Ivan or the black little evil of Raven Tail that attacked Wendy before of the tournament could kidnap them.
In the truth I don’t think that Wendy, Charle and Porlyusica have been kidnapped, counting that at the beginning of the chapter Porlyusica says to Lucy that Wendy was almost recovered I believe that after Wendy awakened the three of them went in another place where thanks to Porlyusica help Wendy will be able to mastered the two spell that Grandine left to her.
Perhaps they will came back just in time to participate at the fifth day of the tournament.
About this two new spell I have two ideas.
One could make her able to fly, counting that she is the dragonslayer of the sky, but in the truth this spell would be useless counting that she has already Charle for this.
The other could be a spell that could make her able to clear the air, to remove the pollution.
In this case both her attacks power and defense power would increase.
But perhaps this spell could be used only for her attacks, perhaps will be the second spell that could increase her healing power.
Anyways if as I believe the smell that Natsu does not know is that of Lucy, if for some reason he forget Lucy’s scent, I don’t think that this his made by the white-knight.
If this will be the case there is the possibility that he will met Lucy, and that he will not remember her, while the other member could remember her, and in someway Natsu could regain her memories.
If this will happened, Charle could says her premonition to the other and in someway the plan of the knight will be stopped (obviously if Charle will return in time).
But there is even the possibility that later, in the next chapters even the other member of the guild, and the audience could forgot her.
If this will happened Lucy could disapper, she could be sucked by the earth and she could reappear immediately after the the destruction of the king palace.
If this will happened she could be accused of having destroyed the king palace, so her only solutions would be that of ran away as a fugitive (this could happened even if my theory about the fact that Lucy will be forgotten will be wrong).
But probably after her reappearance the other Fairy Tail wizard and even the other people could regain her memories.
If this will be the case perhaps all the guild could be accused, if this will happened the guild mght be disbanded, and the member could join other guild
Obviously Lucy will not be able do join other guild of the light, and perhaps even Natsu and Erza will not enter in other guild, in fact the 3 of them coud join Crimoire Sorciere, they could help them in their searching for Zerff.
This could even explain why Levy in the Charle’s vision would have write a letter to Lucy, because Lucy and Levy were in different place.
But in the truth I believe that this time Charle’s vision will not happened.
In fact in the last arc, I believe that Charle’s vision had the only purpose to add curiosity about the arc.
I think that Charle’s vision will not happened because I think that Fairy Tail with the help of Gerard, Urtear and Meldy will be able to stop the evil plan of the knight.
In fact I believe that would be useless having someone that can see the future and not able to change it, just like happened in the last arc or even in Edolas arc (in fact even if Shagotte saw that the islands in the sky where the Exceed lived would fall on the ground she was not able to prevent that this occurs).
I believe that the plan of the knight will be stopped even because there are Mavis (which already detected a malicious force http://www.mangareader.net/fairy-tail/267/17, even if perhaps the force that was feeling was by Raven Tail) and Urtear, Meldy and Gerard (which the they already know about the misteroius force).
So if my theory about Lucy will be wrong I believe that Charle afer the end of each days (at least of the first four days) of the tournament will have a vison.
Every visions will contain some new particulars, and thanks to this they will understood the evil plan of the knight, and they will be able to stop it (I wrote they because I believe that Charle will tell about the visions even the others, not only just to Porlyusica).
But if my theory will be correct there is the possibility that Natsu (and after him even the others) will regain her memory back before that Mercury’s palace would occur.
I would be really happy if Natsu will remember Lucy thanks to Flare.
In fact Flare could hate so much Lucy that she will not be able to forgot her.
If this will happened she could ask to Natsu and the other where is Lucy.
After this question Natsu will remember Lucy, perhaps even thanks to his scarf.
In fact he could detect Lucy’s scent in the scarf, in fact Lucy touched several time Natsu’s scarf, and so Natsu will reagain his memories and after that he could even find Lucy herself.
If this will happened there is the possibility that Flare will be expelled by Raven Tail guild, and then she could join Fairy Tail or at least Crime Sorciere.
There is even the possibility that Lucy will not be accused of the destruction of the palace, but perhaps even she could save the king (perhaps Gemini will make a tunnel or a hole on the ground and there she will put the king while the palace will fall).
This arc is really going to drag on isn't it.
it is a tad predictable and some of the new mages are a big dissapointment, but overall this seems to be a good arc to me, and the longer it goes on the longer fairy tail manga goes on