Wrap-up: The Making Of This is it. This is the one. Find your wife
This is not a solution to the puzzle, but provides notes from its poster. This type of answer has been approved by the community.
Caution: This post may contain spoilers.
For a similar post, see the wrap-up on the sequel - This is it. This is the one. Save your wife. Caution: post also contains spoilers.
Inspiration
I have a fondness for the steganography tag, although I didn't know it existed when I made this. I've always found it impressive how simple things can end up containing hidden messages. I wanted to try my hand at one, but I didn't want it to be too simple. I started out with the basis that I wanted to create a multi-layered puzzle which involved hidden messages.
I got the idea to use IATA codes to hide a message from Tom's puzzle - Which country is INDIA in?. I didn't want it to be too similar though so I included gates and flight times as well.
The story itself came from Khale Kitha's puzzle - Fwd: Re: Karen is missing! I liked the idea of having a story line where you need to find a missing person by solving a puzzle.
Creation and Evolution
I started of with the simple part - the paragraph. I started writing having decided I wanted every ninth word to give a message, and the first letters to say 'COUNT NINE'. Afterwards I decided to make it even more obvious to have 'hidden message in first letters' in italics. However, I wrote this in word and made it italics there, but that didn't transfer to italics here, so I had to add it in later when I realised.
With the first part of the puzzle done I went on to the parts which actually told you were she was. I already had the plane timetable idea, but I wanted something more. I came up with the idea of hiding a message in an actual piece of writing. I came up with the message I wanted - 'try the list of flights', but finding a piece of writing that both had the right amount of lines, and the right letter in each line. I tried several different poems and several different messages, but none worked.
When I got to Requiscat I still couldn't make a message work. I was almost ready to give up and try something else when I had the idea of having the message backwards. After a few attempts, I finally found a message that worked. That felt really good...
With the message done, I wrote done the number of each letter. I didn't want to just list the numbers, so I thought to make them into sums. I then thought of the problem of what the sums would equal, and solved this problem by making them equal 'CLUE' in A1Z26.
The hardest part was always going to be the flight schedule. I broke it down into 4 things that I wanted - The IATA codes to give a name, the flight numbers to say something, the gate numbers to say something and the rearranged flight/gate numbers to give a place.
I then needed ways to rearrange the IATA codes and the rearranged flight/gate codes. To keep on the flight schedule theme, I decided on flight time and adding numbers to the gate numbers, which made me settle on having the rearranged flight number give a message.
I started with the name. MRS was a good starting point, and it needed to be quite a long name so that the other messages fitted. I thought about the message which when rearranged would give a place, but realised that whatever message would be too short and wouldn't give an exact location. So I added TET FRANCE to the IATA codes, because the letters in FRANCE were divisible by 6 and so was TET. I then realised that I wouldn't be able to have a house number in the flight number, so went for Roman Numerals.
At this point I hadn't actually assigned the wife a name, but thought that '?? IS CODER' would be a good message. An anagram search resulted in 'Rodes' and CI. Adding 'LX' gave CXLI Rodes and LX IS CODER, so I made the wife Lucida Xavier. The gate number message was simply 'SAVE ME PLZ', as that matched the number of letters and I scrambled the IATA codes depending on gate number.
Resources
You may be able to tell from the images that I made them in Microsoft Word and took screenshots. I also relied heavily on Google Maps, and a Roman numerals converter.
Takeaway
If you want to create a similar puzzle then here's some advice for you, from the things I learnt making and posting this:
While this phrase may have become a cliche, it is oh so true. There were several times throughout creation were I thought that something wouldn't work, or that there was nothing that would fit. But I persevered and eventually found something that worked in all departments. So my advice here would be to keep trying.
Try and make a habit of checking puzzles after making them. There were several errors I found which had to be dealt with, and even when I posted the puzzle having double-checked there were more errors pointed out. If possible get someone else to check for you, they are less likely to overlook something if they don't know the solution.
If you have created the puzzle, and then find an error which means you have to recreate the entire puzzle, then don't worry. The best puzzles will take a long time to make, and an even longer time to perfect. So if you have to, start from scratch, but keep going. It's worth it.
You may have made the puzzle, but I can guarantee there is something that can be made better, or that there is something that can be added. Look over your puzzle and think 'what is missing?' and put it in.
Take feedback into account for future puzzles, work out what worked well and what didn't, and make your next puzzle even better.
If you write your puzzle in another program or app, then check the formatting when you paste it. As I mentioned above I pasted some text with italics but the italics were lost. Formatting can generally always be improved to make the puzzle look nicer, so look at the preview before posting.