I picked up a yellow card during an encounter in an outer world, from the king in yellow expansion, that states I must discard a thome or lose all my clues!!!

My question is: can I use carcosan page to acquire a thome from another investigator, or I'm late now?

I hate that enounter. It led to our downfall in a recent game. And it's an "Other" encounter, no less! Joy.

To answer your question, you are sunk. Carcosan Page can only be used during Upkeep. Sorry for your loss

Actually Carcosan Page says "Any Phase", so you could use it during the OW Encounter Phase. However, I am under the impression that you cannot use card effects in the middle of an encounter unless they react specifically to such an encounter (like Tablet of Bast, Rerolls etc.)

Here's the relevant part from the FAQ:

Q: When can a character perform actions during a phase?
For example, if a player with the ally Duke (“discard to
immediately restore your Sanity to its maximum”) draws
an encounter and has to roll a die and lose that much
Sanity, when can he discard Duke to restore Sanity: not at
all once the encounter card is drawn, before the roll, or
after the roll?
A: Actions can be performed at any time during their
listed phase as long as any given conditions are met.
However,
once an encounter is drawn, it must be resolved
before any more actions can be performed. So, in the
case of Duke, you can use him before or after drawing an
encounter card, but if you draw the encounter card and it
inflicts Sanity loss that reduces you to 0 Sanity, you go
insane before you can use Duke. Flesh Ward is one exception
to this rule because it prevents a Stamina loss and is
intended to be used in response to such events.

I thought mine said "Upkeep." "At the start of your turn..."

Maybe I was thinking of Lambeau's Witch Blood .

But upon this further reflection, I'd agree with Morgaln. If you can't mitigate a sanity loss or prepare for an imminent loss with Duke, you can't use the C.P. to say "no no wait here... I have a tome with me somewhere..."

Same boat as Duke once your draw your encounter its to late unless its something like Flesh Ward, next time just grab the tome before you draw the OW card then give it back when you leave the OW.

Yep, too late to use the Page. Once an encounter starts, it must be finished before using another card effect.

Morgaln said:

Thank you, you're right.

Luca