Evensong
The Enterprise-D conducts a study on a nebula in the currently uninhabited Trion system, but strange, curiously regular beams of electromagnetic particles interfere with their scans. They investigate further, and learn that the particles originate from a device somewhere inside the nebula. The device, on closer inspection, seems to be a decrepit, pre-warp space probe, designed to emit these particles constantly, with seemingly no purpose. Meanwhile, Data participates in a concert given by members of the crew, and wonders at the unifying power of music.
Picard uses his knowledge of archeology and the ship's sensors to analyse the beacon, and comes to the conclusion that the beacon is millions of years old, while Data enlists Troi's help in discovering what, exactly, it is about music that brings people together. Geordi and Data believe that the electromagnetic particles were intended as a form of communication, but due to the ion interference in the nebula, they're unable to decode its message. But with no other civilization present in this system, who placed this probe here, and why?
They discover that the probe was deployed by a long-dead alien race who used to live in the Trion system, in an attempt to find and communicate with any life that might be out there with them in the universe. The ancient race must've been one of the earliest species to develop into a sophisticated society and achieve spaceflight, but unfortunately, due to this fact, they were too early to find another species with the ability to detect or reply to their message. Instead, they died out without ever meeting another species like them, but their probe continued broadcasting their message, and their search to find another, similar soul in the universe lived on.
Picard has a Moment™ and gives a speech about the importance of discovery and scientific exploration. The ship catalogues the find, and sends a report back to Starfleet. They leave the probe as it is, calling out to the rest of the universe.
Next episode: Precipice