It's from The Next Generation's Third Season and is an episode called 'The Defector'
Picard is given information by Admiral Jarok, which turns out to be a lure for a trap. Tomalak is there waiting to take the Enterprise, intending to display its broken hull on Romulus. Worf under orders, has been secretly communicating with the Klingons (a line of dialog from Picard earlier in the episode appeared to be throwaway but actually formed part of the climax).
It's worthwhile watching 'The Enemy' a couple of episodes before this, in order to appreciate more from the story... but 'The Defector' works without any prior knowledge. This year of TNG is probably my favourite. The show suddenly firing on all cylinders, after the mixed quality of Season 1 & 2.
