Solution: To-do List
Answer: COFFEE POWDER

Written by Tan Chor Kiang

First, solvers need to realise that the lists of words are actually ordered lists, each with an odd-one-out item (as the flavourtext also suggests). The item can be corrected by changing a letter. This allows you to extract a single letter from each ordered list. The easiest way to arrive at this aha is through the “PRISONER, GOBLET... HOLLOWS” list, which is of keywords in the titles of the well-known Harry Potter series.

The lists of words were given in alpha order; the list of number series below then provides a mechanism to reorder them. In the Harry Potter example, PRISONER corresponds to the 3rd book in the series, GOBLET to the 4th, and so on. The word to change is HOLLOWS, which should be changed to HALLOWS. This corresponds to the series “3, 4, 5, 6, [7]”, where the number in brackets indicates the word in the sequence that needs to be changed.

The extracted letters, in number series order, give the final answer COFFEE POWDER.

The full list of ordered lists and their categories can be found below.

List Category Wrong item Corrected Extracted Letter
WHEEL, CALL, COLUMN, SENSE, HEAVEN Idioms with ordinal numbers (third wheel, etc) CALL WALL C
SALMON, MNEMONIC, DAMN, PEOPLE, COOP Words with silent letters (alpha order by silent letter) COOP COUP O
FEBRILE, FARE, APRON, MAYOR, JUNK Words starting with month abbreviations FARE MARE F
CLUMSY, QUIET, RUSH, FALL, WORRY Mr Men books FALL TALL F
MITIGATE, FARTHER, SOCIAL, EASTER, TILLER Words starting with musical notes (solfege) EASTER LASTER E
BULLETS, DECKS, TREYS, SAILBOATS, NICKELS Poker pair nicknames DECKS DUCKS E
REFUTAL, RAGE, HAGGLING, GLOOP, CONSENT Stages of grief (synonyms) GLOOP GLOOM P
PRISONER, GOBLET, ORDER, PRINCE, HOLLOWS Keywords in Harry Potter book titles HOLLOWS HALLOWS O
BOLD, COPY, BOOKMARK, CENTER, WIND CTRL functions WIND FIND W
LAY, SWIM, MILK, DANCE, LEAD 12 Days of Christmas LEAD LEAP D
CUT, FLY, SURF, STRENGTH, FLESH Pokemon Gen 1 HMs FLESH FLASH E
KIDNEYS, SUPERGLUE, BURTON, MOOSE, WASPS Dumb Ways to Die BURTON BUTTON R