# PSE Advent Calendar 2021 (Day 19): Santa's Dilemma

This puzzle is part of the Puzzling Stack Exchange Advent Calendar 2021. The accepted answer to this question will be awarded a bounty worth 100 reputation.

< Previous Door Next Door >

It was late in the night when I heard a whoosh from the chimney, which turned out to be a tall, old man. I stood up from my table of puzzles that I was trying to solve, and walked cautiously towards the man. But then, the doorbell rang. I quickly ran towards the door, still eyeing the intruder, and slowly creaked the door open, ready to close it again... except outside was Ingrid Deduction, with her backpack of her essentials: laptop, pens, and paper.

"Well, what a pleasure it is to see you again!" Ingrid said, as she walked into the room. "I suppose you saw Santa Claus?"

"Santa Claus? Where?" I asked, surprised.

"He's over there," whispered Ingrid, pointing to the tall, old man.

Shocked, I walked to shake his outstretched hand. I scurried away to Ingrid, and sat down on my chair.

"So, what happened that you had to come tonight?"

"Well, my sleigh got broken while I was starting to pack my presents into the sacks... So I needed to find Bob Sleigh, my sleigh fixer. But, I couldn't find him on the North Pole, so I went to try find him around here, and that's how I found Ingrid. She said that I might have something around here that might help. You see, this is a dilemma as without presents, the Christmas Spirit goes down! And... if Christmas Spirit goes down... war will happen."

I was shocked and terrified at the same time. I turned to Ingrid. "S-so?"

Ingrid, replied "So, did you see anything out of the ordinary? Something that you don't remember having?"

I thought for a second about Bob Sleigh, then remembered. I had a piece of paper here that had Bob Sleigh as its title. I turned, and quickly opened my closet full of paper. After a few minutes, I found it, the piece of paper with a puzzle and some jumble of letters that could have been elvish.

"Here! Does this help?"

Ingrid quickly opened her laptop and with a sad smile, turned to Santa.

"I think you need to see this."

Santa expression was grim, and with a whoosh he was gone.

What happened that made him go?

Esbj Devzh, J on hcsjgimm hgyi enlo mpm dim zojg. J olw kgwuiswo, evj abyff mekq ap hiw Yszzo Qcmw mc zgpessk. Elme hss ujjmvm ap guwlp gubs smnpw, itk zcvj ssuk. Nfh csno, itk toww fw. Bnl coovtxa choh ug hvmir uvf zltxoufgt xzv Knyjguelw. Yapdy!

### SOLVER NOTES

Thanks to Stiv for letting me borrow Ingrid for a bit of colour!

Despite having a holiday dressing, this puzzle is just a sudoku with letters (and more) .

• There are 9 letters

• The 9 letters appear in each box, row, and column once.

• There is a logical solution to the Sudoku, and should be written in the answer. (and more)

I hope you enjoy!

Box 1 resolves instantly:

R1C1 is the only place for G, R3C3 the only place for D, leaving R3C2 as B.

Box 9 resolves similarly:

R7C7 is the only place for G, R9C9 the only place for D, leaving R7C8 as Q.

Some additional cells are forced as naked singles in their boxes:

R1C7(J), R2C5(Q), R3C9(Z), R4C2(Y), R8C1(Y), R8C4(D), R8C5(G), R6C6(G), R4C3(G), R7C4(B), R7C6 (T), R9C6(J)

Some more easy stuff, but getting tougher to find:

R7C1 must be Z (naked single in row); R9C1 can only be Q, forcing R6C1 to be J and R9C3 to be B; R3C4 can only be T and R3C6 can only be Y; R5C6 is only place in C6 for Z, forcing R2C6 to be D and R1C4 to be A; R1C9 is now T

In C9, A is the only possibility for R2, and Q for R4; this completes box 3, with R2C7 B and R2C8 Y. In C7 this leaves R6 the only candidate for A, forcing R4C7 to be D; now in R4, C4 cannot be Z so it must be J, forcing R4C8 to be Z; in C8, R6 cannot be J, so R5 is J and R6 T; box 5 completes with R5C4 Q and R5C5 B, and then row 6 completes with R6C2 Z and R6C3 Q. The grid:

At this point:

There is not a unique solution to the Sudoku...except there is, because I realize I forgot one of the clues when I transposed it. The final grid:

Where do we go from here?

Five of the grid entries are highlighted, which suggests that these characters might form a key to the cipher text given. Vigenère seems the obvious choice for a cipher, and using the tools at DCODE suggest that the ciphertext might be a Vigenère cipher with a key length of 5.

But trying the obvious choices (top-to-bottom, left-to-right) as a key yields gibberish. So let's try something else: the introduction. It sure looks like it should be "Dear Somebody,", so let's look for four key letters that decode "Esbj" to "Dear", which gives "BOBS". Hmm...that seems relevant somehow. Let's try the key BOBSLEIGH...and it works!

The secret message decodes as: "Dear Santa, I am probably gone when you see this. I was captured, and taken back to the North Pole by raiders. They are trying to steal your elves, and your home. Get back, and save us. The bandits want to wreck the happiness for Christmas. Quick!"

So the question remains:

Was the sudoku just a red herring, or is there a tie I'm not seeing? I tried decoding the yellow squares using the BOBSLEIGH key, and also the word "Quick", which appears prominently at the end of the message, as both the key or the plaintext, but I'm not getting any further connection.