Yes, CONSPIRACY is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, N 1, S 1, P 3, I 1, R 1, A 1, C 3, Y 4.

Is it a valid word?

CONSPIRACY is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a secret agreement between two or more people to perform an unlawful act
a plot to carry out some harmful or illegal act (especially a political plot)
a group of conspirators banded together to achieve some harmful or illegal purpose