The Reptilian forces Hoshi through brainwash to decipher the code of the Aquatics and activate the weapon with the Insectoids and their own codes. Archer manages to convince the Aquatics to help them against the Reptilian, promising to help them to destroy the sphere system in the Expanse. The Humanoids, the Arboreals and the Aquatics join the Enterprise and they battle against the Reptilian and Insectoids. Meanwhile Major Hayes and his team are beamed to the Reptilian vessel where Hoshi is imprisoned. When the enemy is near to be defeated, the Sphere-Builders cause a strong anomaly destroying many ships and allowing the Reptilian to escape through a vortex.
"Countdown" is another engaging episode, with a great star battle and dramatic fate of important characters. The saga of the Enterprise in the expanse seems to be near to the end with many casualties. My vote is eight.
Title (Brazil): "Contagem Regressiva" ("Countdown")