The Sentinels was a failed TV venture that folded after the production company lost all their materials in a warehouse fire. However, to salvage funds and to attempt to generate enough interest to continue the project the frist three episodes were released as a pilot movie. The project was never completed, the novels by Jack McKinney are available through the end of the Sentinels Saga.
15 years after the destruction of the SDF-1 and SDF-2 at the hands of Kyrhon the REF (Robotech Expeditionary Forces) head to Tirol, homeworld of the Robotech Masters, in hopes to find a peaceful solution before Earth is drawn into another devastating war. However, when the SDF-3 and REF Fleet come out of hyperspace fold Tirol is under seige by a new alien threat- the Invid! What the REF learns is that the Masters have left, taken nearly all of their able and combat ready society with them, to Earth! The SDF-3 was damaged in the battle with the Invid so they are unable to fold home, however several ships (Col. Wolfe) are sent later to assist Earth once it is confirmed that Earth is fighting the Masters.
What begins in Tirol is a battle for freedom amongst various races in that quadrant of the galaxy. The battles begin with liberation of several alien worlds and the formation of a the Sentinels (a freedom force led by the REF and alien freedom fighters who came to the REF for help). The saga (from the books- as the tv movie ends with the battle of Tirol and the SDF-3 being crippled) continues to a battle across half a dozen worlds and a climatic battle between the Regent and Breetai. Breetai is killed in the battle, however he is successful in killing the Regent and ending the war. The REF Fleet returns to Earth in time to be utterly demolished by the retreating Regis at the end of the Invid occupation of Earth. The SDF-3 never appears with the REF fleet and is presumed lost. Scott Bernard and a handful of others take the Ark Angel and begin a trek across the galaxy to locate the SDF-3. The saga of Robotech has finally come to a close.