Tess Harding first appears in Roswell’s season 1 episode Crazy. Although she is from the same pod set as our alien protagonists, she hatches later and consequently is not integrated into Roswell when they are. Nasedo is, however, waiting for her, and as Ed Harding he both hones her powers and gives her a broader understanding of her heritage on planet Anatar than the other aliens have.
Tess’s particular power is mind-warping, enabling her to alter –sometimes substantially –a person’s memory. While the experience can prove unsettling, especially to her fellow aliens, it does have it’s advantages, as when she is able to remove Larek’s memories from Brody Davis’ mind.
Initially in season 1 she befriends Isabel, bonding with her over a shared love of over-sweet coffee and Tabasco sauce. When her alien identity emerges though, not only Isabel but the others also become suspicious, believing Tess responsible for the handprinted victim discovered in 1959. It is not until Four Square when Tess takes Max to the desert for answers that he realises she is not in fact the shapeshifting Nasedo, although even then he is reluctant to trust her. This changes when on Max’s request Tess begins to help him remember his alien home; he remembers not only Tess as she was on Anatar but his wedding to her and love of her, cementing a tentative friendship.
Following the death of Ed Harding Tess comes to live with the Valentis. She is especially close to Kyle, who calls her his ‘favourite Martian’ and comes to think of her as a sister. When Tess’s efforts to decode the book brought with them from Anatar lead to devastating consequences, it is an unwitting Kyle she enlists to help her.
Tess leaves Roswell in the season 2 finale Departure, having seemingly secured a future for herself on Kivar’s Anatar. This is not the last we see of her, however; Tess returns towards the end of season 3 bringing chaos and confusion, and a hefty dose of self-sacrifice with her.