The Lost Year (Empath stories)

The Lost Year is the time in Empath's life that occurred around his 155th and 156th birthdays, when the events of the Smurfed Behind saga took place.

Prelude
Some time prior to the events leading to The Lost Year, Empath and several other Smurfs were called upon to rescue a book that belonged to Father Time called the Tome of Tomorrow, which would give whoever reads the book glimpses into the future in order to shape events according to their desires, although in reality events recorded in the book are considered unalterable. Father Time warned the Smurfs not to open the book under any circumstances. Although the Smurfs were faithful in this regard as they retrieved the Tome of Tomorrow from those who have stolen it, Brainy had accidentally caused the book to be opened, and to the page it was opened, the Smurfs present saw that the entire Smurf Village was sucked into a vortex that transported them through time with no certainty of ever getting home.

Empath's 155th birthday
Shortly before Empath's 155th birthday, Empath was summoned to do some errands for Homnibus the wizard in retrieving some vital elements for his experiments. During Empath's absence from the Smurf Village, Snappy, Hefty, Brainy, and Tracker had awakened a baby dinosaur named Crinkles and tried to take care of him, only to realize that he was unable to eat the food in the present time that was offered to him. Uncertain of what to do, Papa Smurf and Grandpa Smurf visited Father Time, who gave them the Key of Chronos, a time-traveling device that would enable the user to open portals between one time period and another. Papa Smurf used the key to open a portal to the prehistoric era that Crinkles had come from with the intention that he and Grandpa Smurf would travel alone with Crinkles to find his parents. However, upon opening the portal, it ended up drawing all the other Smurfs, including Puppy and Smoogle, into the vortex and they ended up in the same time period as Papa Smurf and Grandpa Smurf. Only Polaris Psyche was left alone in the village, as the portal had closed up after the last Smurf was sucked in. It is presumably during this that the Key of Chronos was destroyed and the timelost Smurfs were left with the chronosyte crystals that powered the key, forcing Papa Smurf to find the proper arrangement so that he could bring all his little Smurfs back home, leading to the adventures they had as chronicled in the Season 9 episodes of the cartoon show (with the addition of many other Smurfs).