A spatial anomaly in the Devron system that grew backwards through time and threatened to stop life from ever arising on Earth, which Jean-Luc Picard had to solve across three periods of his life.
The anti-time anomaly is the puzzle at the heart of All Good Things..., the final episode of The Next Generation. Picard finds himself slipping between the present, the days just before the Farpoint mission seven years earlier, and a future twenty-five years on in which he is retired and ill.
In each period a disturbance appears in the Devron system near the Romulan Neutral Zone, and it is largest in the past. Q reveals that the trial of humanity never ended, and that Picard himself will be the cause of mankind's destruction. The anomaly is a rupture of time and anti-time, created when three versions of the Enterprise each scan the same spot with an inverse tachyon beam.
Picard persuades all three crews to fly into the anomaly and collapse it with static warp shells, at the cost of the ships. The timelines reset and Q admits that he gave Picard a helping hand.