“The Die is Cast” is episode twenty-one of season three of Star Trek: Deep Space Nine.
In the previous episode, “Improbable Cause”, it was discovered that the person who attempted to get Garak killed was his old boss, Enabran Tain. Tain, after Garak and Odo found him, invited the former to join him, as he comes out of retirement to go on a mission. Garak agrees, pleased to be with his old mentor.
The Cardassian Obsidian Order and the Romulan Tal Shiar, a similar organisation, have joined forces to launch a pre-emptive attack on the Founders’ homeworld, with the intention of killing them all. Without the Founders, the Jem’Hadar will lack the drug they need to survive, and will quickly die.
The attack is being done without the permission of their respective governments. The fact that the Obsidian Order was building their own ships was discovered by Tom Riker in “Defiant”.
Of course, it’s not going to be that easy. Starfleet dispatches ships to DS9 to prepare for whatever the outcome of the attack is, and Sisko plans to go looking for Odo.