it was suggested in a memo that Mark Lenard could appear as Spock's on-screen father, Sarek. Lenard had made his first appearance as Sarek in the Star Trek: The Original Series episode "Journey to Babel". Trent Christopher Ganino and Eric A. Stillwell began to work on a script involving both Lenard as Sarek and Denise Crosby as Tasha Yar. This was because Crosby told Stillwell that she wanted to return to the show after her character was killed off in "Skin of Evil" in the first season of The Next Generation. This script would change over time to become "Yesterday's Enterprise". Ganino and Stillwell's original pitch for "Yesterday's Enterprise" featured a team of Vulcan scientists, led by Sarek. They accidentally travel to the past using the Guardian of Forever (a time portal seen in The Original Series episode "The City on the Edge of Forever") and kill Surak, the founder of modern Vulcan logic. When they return to the present, they find that the Vulcans are allied with the Romulans and at war with the Federation. Only Sarek and his Vulcan scientists are unaffected by the change, and so he elects to return to the past and replace Surak, allowing the timeline to be restored. Michael Piller was not happy with this script as he wanted the episode to be more centered on The Next Generation cast; as such, Sarek and the Guardian were dropped from the story. When it was pitched by Marc Cushman and Jake Jacobs, the idea which formed the basis for "Sarek" featured an original character instead of Sarek. The staff writers felt the degenerative disease concept would be a subject that viewers could relate to, as it could be a metaphor for dementia in the elderly. The element of the plot wherein the disease would cause telepathic problems for the rest of the crew was then developed, with Sarek added to the plot at a late stage in order to ensure an emotional impact on the audience. Piller said that "it brings home the idea that even the greatest of men is subject to illness". He also said that the plot was a direct reference to the declining health of Roddenberry. The script was written by noted fantasy author Peter S. Beagle, best known for his 1968 novel The Last Unicorn. Because of the chronological differences between the settings of The Original Series and The