Message in a Bottle

Seven of Nine finds a vast, ancient network of alien sensor relays reaching as far as the Alpha Quadrant, where it detects a Starfleet vessel. Attempts to send a message fail, so Janeway transmits the Doctor's program instead. He materialises aboard the USS Prometheus, a secret experimental warship, only to find that Romulans have killed the crew and taken control. The Doctor activates the ship's own Emergency Medical Hologram, a newer Mark II model with a very different manner, and the two bicker their way through a plan to retake the ship by flooding it with anaesthetic gas. Stumbling on the ship's multi-vector assault mode, they help defeat the Romulan force as Starfleet ships close in. Meanwhile the Hirogen, who claim the network, demand that Voyager disconnect from it. The Doctor makes it home with wonderful news: Starfleet knows Voyager survived, and the crew are no longer alone.