ENT Season 3 Episode 15 Harbinger

Plot

It is December 2153, and Enterprise continues along its course towards Azati Prime to find the Xindi weapon.[a] Commander Tucker begins spending time with a female MACO, and Sub-Commander T'Pol begins to exhibit signs of suppressed jealousy. Meanwhile, the long-simmering tension between Lieutenant Malcolm Reed and Major Hayes finally comes to a head when Hayes approaches Archer over their security roles aboard Enterprise. Hayes suggests training together to share ideas, but Reed sees this as a move to undermine his authority.
Enterprise diverts to investigate a convergent region of spatial anomalies (created in the center of five spheres), where the crew discover a pod containing an alien. The pod is retrieved, and the alien is taken to Sickbay, but Doctor Phlox can do little to keep him alive. Archer wishes to interrogate him, and does so against Phlox's wishes. Meanwhile, Hayes sets up a weapons training session, and comments continually at Reed's performance. They later get into a fistfight, much to Archer's chagrin.
T'Pol and Tucker finally continue their Vulcan 'neuropressure' sessions, and T'Pol reveals her conversation with Sim-Trip to him, and the two become intimate. She later is very clinical in thanking Tucker for his assistance in her one-time "exploration of human sexuality". Back in Sickbay, the alien revives and physically begins to phase. He attacks Phlox, and then heads through walls towards the warp core, attempting to destabilize the magnetic seals. Reed and Hayes, now working together, stop the alien and he is returned to Sickbay. Archer wants answers, the alien says that when the Xindi destroy Earth his people will prevail, and phases again, disappearing completely.