So if another investigator plays this on my Investigate test, do either of us get the additional clue if the test succeeds? It seems to me that you could argue for all three answers:

- I am doing the investigating, so I should get it,

- She's playing the card, so she should get it,

- Neither of us should get it, because she played the card, and she is not eligible to get any clue (including an additional clue)

From the unofficial FAQ (confirmed by the designer):

11) When one player commits a skill card to another player's test, if that skill card adds an extra effect on top of the skill test's normal effect (e.g. "draw 1 card" on Guts, "heal 1 horror" on Fearless), then the player who committed the card resolves that effect. If the skill card modifies the normal effect of the skill test (e.g. "deal +1 damage" on Vicious Blow, "discover 1 additional clue" on Deduction), then the player who performed the skill test resolves it.

Wow, that's not obvious at all based just on the plain language of the rules. Thanks.

So in this case then if I am investigating and someone else plays Deduction, I get the additonal Clue?

Quote: If this skill test is successful while investigating a location, discover 1 additional clue at that location.

If the Location has only 1 Clue, does this work? Does the Clue come from the "Token Pool" (I can't think of a better way to describe it).

And if yes, if there were 2 Clues at the location, does it only take one Clue from the Location, and one from the Pool?

Deduction gives the investigating character the extra clue.

Like all clue gaining player cards in the game, none of them take clues from the bank. If there's no clues on the location, you cannot gain any clues. So don't play Deduction for an additional clue if there's only one on the location (you certainly can still commit it for the Intellect boost if you want to at a one-clue location).