Strange signals start coming from Epsilon 3, the planet below Babylon 5. A science ship is sent to investigate, but is fired upon by a defense system on the planet. Meanwhile, Garibaldi worries about a lover he left back on Mars, when fighting breaks out there.

The situation heats up when an Earth Force heavy cruiser arrives to "protect Earth's interests", and the fusion reactors on Epsilon 3 start going out of control, and may blow up the planet and Babylon 5.