XCOM: Enemy Unknown

After developing a weapon that allows the capture of live alien specimens and building a facility to house such captives, XCOM's head of research Dr. Vahlen requests that a live alien be captured for interrogation. Capturing one and conducting the interrogation reveals vague information about the Outsiders, crystalline beings encountered aboard UFOs that are shot down. Dr. Vahlen then requests that XCOM capture an Outsider for study. The Outsiders are discovered to be similar to antennas, receiving a signal broadcast from a location buried underground. XCOM dispatches a team to investigate the signal; it is found to be coming from an alien base where experiments are performed on abducted humans. During the mission, the base commander's psychic communication device is recovered and reverse engineered.
The device reveals a previously-hidden "Overseer" UFO, which when shot down is found to hold powerful psionic enemies, called Ethereals, and a strange psionic artifact. Once the Overseer is shot down, the massive enemy "Temple Ship" reveals itself and attacks the Earth, causing earthquakes even as far away as XCOM HQ. The reverse-engineering efforts enable XCOM to unlock the latent psionic powers of its own troops, and through them to attack and board the Temple Ship, using one "Volunteer" who taps into the alien hive mind. During the final battle aboard the ship, the Ethereals reveal that they have been testing and experimenting on other species, searching for a race that is perfect in mind and body, and that the various aliens the player has encountered have all been failures in the Ethereals' experiments. By feeding humans their technology a few steps at a time, the Ethereals allowed humans to evolve to a fuller potential, and believe that humanity may be the culmination of their search, to find the perfect army to fight a threat more dangerous than the Ethereals. Because of their own failure to evolve with the rest of their species, they intend to dominate the human race and use them to further their own evolution in the hopes of fighting the unnamed threat. After slaying the leader of the Ethereals, the Temple Ship begins to self-destruct, and the psionically-gifted volunteer takes control to fly it high above Earth, where it explodes while the rest of the boarding squad escapes.