Eoin Davey.

- MSc. Mathematics @ Universiteit van Amsterdam.

- Former SRE @ Google.

- Éireannach.

With 3 puzzles down we are into the 2nd half of the puzzles.

Our first foray into the latter half presents us with this website.

All we get is some text telling us to find the next infinity stone and these 3 mp3 files

The 3 audio recordings are of phone calls, ostensibly from the Avengers to various geology departments in Fort Smith, Syracuse and Idaho.

After spending some time on spectrogram analysis and other audio analysis techniques I became quite sure that the key lay in the 10 tones at the start of each recording.

Generating a chromagram from the sequence of tones shows us that each tone is a perfect musical note.
Here is the chromagram for the Idaho phone call.

We can see from this that the notes for the Idaho call are `A#, F, A, D, A, C#, A, C, B, C`

Doing this for each call we get the following notes.

fort_smith.mp3 | D, C#, D#, B, F, B, A, A#, C, D |

syracuse.mp3 | C, B, E, A, A#, B, D#, A, C#, C |

idaho.mp3 | A#, F, A, D, A, C#, A, C, B, C |

What if these tones represent the phone numbers being called?.
We can find online that the area codes for Fort Smith, Syracuse and Idaho are 479, 315 and 208 respectively.

This gives us a mapping of notes to numbers because we now know the first three numbers of each call.

0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
---|---|---|---|---|---|---|---|---|---|

F | B | A# | C | D | E | ? | C# | A | D# |

We know from the phone call recordings that it’s the Idaho geology department who know the location of the Infinity Stone. Using our mapping above we can see that the Idaho geology department’s phone number is **208-487-8313**.

At this point I wondered for some time what to do with this number, it took some time before I even entertained the idea that it would be real phone number. But eventually I decided that I had nothing to lose by calling the number, and so I did.

After a few rings, the phone was answered, and a robotic voice told me

GET request /museum to learn the location of the infinity stone.

Visiting this URL greets us with this message.

Your solution is: drive realised worldwide

Puzzle 4 Solved!