Star Trek: The Next Generation: Imbalance

The Jarada are a mysterious race of insectoid being with an extreme devotion to protocol. When this usually reclusive race offer to open diplomatic relations with the Federation, Captain Picard and the U.S.S. Enterprise™ are quickly ordered to Jarada to negotiate the exchange of Ambassadors.
When the ship arrives, the Jarada seem uncharacteristically friendly. They invite Picard to send down members of his crew and negotiations proceed both quickly and smoothly. Suddenly, however, the Jarada change. They cut off Commander Riker and his away team from the U.S.S. Enterprise and initiate an unprovoked attack on the ship, Now Picard must unravel the aliens' mystery before it's too late for the away team -- and the U.S.S. Enterprise.