Star Trek The Next Generation, book 35 : The Romulan Stratagem
Robert Greenberger1995

On a mission to an unexplored planet near the Klingon/Romulan border, the USS Enterprise-D travels to the planet Eloh to negotiate Federation membership. But upon arrival, Captain Jean-Luc Picard and his diplomatic team find themselves face to face with Commander Sela, an old Romulan enemy – who's there to convince the Elohsians to join the Romulan Empire.

When a series of fatal incidents casts suspicion on both delegations, Data must form an uneasy alliance with Sela to prove the innocence of the Starship Enterprise crew – or lose a strategic stronghold to the Federation's greatest enemy.