I just posted a thread on this, but after being on these forums an extra 15 seconds, I found this thread and figured this might be more appropriate here.

I can understand why people might think that this was just Moriarty's way to be dramatic.  Sherlock has caused Moriarty to "fall" as a master criminal, getting in the way of several of Moriarty's cases, and thus Moriarty "owes" Sherlock a fall.

I accept that this is quite possible, but let me entertain another idea that involves a little more intricacy.

The theme of fairy tales came up a lot in this episode, repeatedly in fact.  The major story being Hansel and Gretel, which came up several times from the children, the envelopes with bread, the invisible trail left by the kid, etc.  Moriarty said several things relating to fairy tales.  "Every fairy tale needs a villain" for example.  And also, Moriarty wrote that fairy tale for Sherlock in the cab.  The one that drove me crazy was "I love newspapers, fairy tales.  Grim ones at that".  This drove me crazy because of his choice of word "Grim", or to me more likely "Grimm".

Further, it was a Grimms' fairy tales that Sherlock found in the kids room.  What does this have to do with I.O.U.?  If you do a direct translation from letters to numbers, A-1, B-2, C-3... then I.O.U.  = 9, 15, 21.

The very book that Sherlock is holding has a table of contents, exactly like the one found on the Wikipedia page " Grimms' Fairy tales".  The three stories associated with these numbers are: The 12 Brothers, Hansel and Gretel, and Cinderella.  The fact that out of 86 stories, we get a match up to Hansel and Gretel seems TERRIBLY suspect to me.  Having just read Cinderella, I have having trouble making any further connections than I already have, and thus brings us back to "Moriarty owes Sherlock", but this coincidence makes me feel at least a closer look is in order.

Thanks. I feel like I got two puzzle pieces to fit together, but they don't match the rest of the puzzle.

I have actually seen this, but I prefer the direct translation as it is simpler (less steps) and includes Hansel and Gretel, which I feel is required for this line of reasoning to have any merit.

Well allegedly Mycroft sold out his brother, but we'll see...
Interesting...
But I just thought Sherlock was murmuring at this time because matters were coming to a head and he thought he may die soon.

You just wanted an excuse to use "hemidemisemiquaver," showoff. Wait! Quavers! Call Molly!

I have always asked myself why Sherlock is interested in Connie Prince's cat. He has seen the scratches on the body and he has already solved the problem with Connie's death. Why did he visit Connie's house? To play photoshooting with John? No. He askes even "Is she Connie's?" And he wants to know the name. Sherlock does not do small talk. The pet thing is an important clue. The cat's name is "Sekhmet". Sekhmet is the egyptian goddess of war. She drinks blood. People believe she could bring death.Sekhmet is a symbol of the fighting spirit. Daughter of the sun god Re. Re defeated her by pouring beer, red paint and certain plants -probably containing belladonna and opium- on the ground in order to stop Sekhmet.Sekhnet drank the not-blood. Then it is said that "her heart was filled with joy" and her rage and slaughter was ended.

The name "Sekhmet" can be read in hieroglyphs and you can find some pictures with three symbols that look exactly like our IOU. It's a symbol for Sherlock to see as a death threatening. Obviously the five pips/cases and even the six episodes are full of clues for Sherlock and us to find them.

The hairless cat is a Sphynx cat so the choice of an Egyptian goddess's name for her is logical. Sekhmet is actually a lioness. A couple of things occur to me about the importance, or otherwise, of this cat: firstly it allows John to come up with his own theory of how Connie died (wrong!) and secondly perhaps her being a Sphynx is important in itself. The Great Game is all about riddles, which continues into the Reichenbach Fall, and perhaps the most famous riddle of all is that of the Sphynx. Later Sherlock says he doesn't like riddles to Moriarty.

The hieroglyph for Sekhmet does not really resemble our IOU, it resembles IOn. She is a warrior goddess but also one of healing.

Be wrote:

I have always asked myself why Sherlock is interested in Connie Prince's cat. He has seen the scratches on the body and he has already solved the problem with Connie's death. Why did he visit Connie's house? To play photoshooting with John? No. He askes even "Is she Connie's?" And he wants to know the name. Sherlock does not do small talk. The pet thing is an important clue. The cat's name is "Sekhmet". Sekhmet is the egyptian goddess of war. She drinks blood. People believe she could bring death.Sekhmet is a symbol of the fighting spirit. Daughter of the sun god Re. Re defeated her by pouring beer, red paint and certain plants -probably containing belladonna and opium- on the ground in order to stop Sekhmet.Sekhnet drank the not-blood. Then it is said that "her heart was filled with joy" and her rage and slaughter was ended.

The name "Sekhmet" can be read in hieroglyphs and you can find some pictures with three symbols that look exactly like our IOU. It is a symbol for Sherlock to see as a death threatening. Obviously the five pips/cases and even the six episodes are full of clues for Sherlock and us to find them.

I am sorry. I want to add something that I found out. It's not cool to quote myself.

I think the sekhmet-clue can also be read as metaphor for our female character who is the cat-woman. Look at her blog. She provides the blood on the pavement. Maybe it is Molly.

I think we'll just have to wait and see - I don't think a theory has been put forward which isn't conceivable at this point.

We can only see who is closest now.

-m0r

The use of vowels in a pattern has been used many times over the centuries to convey messages.
Most English speaking people will have learned one little bit by rote really and this could be the subliminal key we are looking for.

You see Old MacDonald had a farm e i e i o . Now the use of the last two letters of this 'catchphrase' ... the " i o " followed by the extra letter " u " could in fact point to the fact that " u " is part of the Farmer MacDonald's farm, hence inferring that Holmes will in fact be transported to and become a part of the aforementioned farm community.

It stands to reason really.