Alissa Strudwick is played by actress Larisa Oleynik. She is Tommy's second serious girlfriend (after August) and probably his one true love. While his relationship with August was always frosty at best, Alissa has a kinder, gentler personality and is also a lot more forgiving. This proves to be an important element as their relationship at times follows a similar line to that between Dick and Mary.
Even though Tommy is the most level-headed and mature member of the unit, his behaviour towards Alissa creates all the usual, embarrassing moments we come to expect and is pretty much of the sort that would test the patience of anyone. Yet she remains chirpy and resolved to work things out. She seems to genuinely like Tommy and they seem so well suited. In fact it is their mutual shyness of each other that initially proves the main barrier in their getting together. And despite the many ups and downs in their relationship, they always seem to be back together for the next episode.
There is, of course a strain on their relationship caused by the fact that Alissa is the daughter of Vincent Strudwick, Dick's fellow physics professor and rival. When Dick decides that the only way he can even scores with Strudwick is by sleeping with his wife (Alissa's mother) Tommy goes along, thinking that it will help him to move things a stage further with Alissa.
Memorable moments in the Tommy/Alissa storyline include Tommy having casual sex with a relative stranger the night prior to when himself and Alissa are supposed to 'do it for the first time' on Valentine's night. Alissa finds out because Tommy openly volunteers the information. Tommy was still a virgin up to that point while Alissa had already had 'experience'. Feeling intimidated Tommy thought a trial run was in order and expected Alissa to fully understand.
Another occasion sees Alissa running into to Tommy and Dick sharing a warm embrace which, while innocent enough, could be misconstrued and is misconstrued on this occasion. We see Alissa running out the door in shock with Tommy chasing after her saying "he's not my dad, he's just some guy I'm living with!"
Eventually Tommy and Alissa do break up but not because of anything that Tommy does. Instead fate intervenes in the form of Sally. Misinterpreting a casual remark that Alissa makes, Sally thinks that she is about to break up with Tommy. Sworn to her duty to protect and defend the unit, Sally decides to get in first and break up with Alissa on Tommy's behalf.
They do show signs of getting back together in season six (the final season). They spend a Halloween night together watching a scary movie. This is part of Tommy's plan to get back with her and which almost works except that he's the one who ends up getting scared.
In the final season Tommy goes off to university. Whatever feelings he may still have had for Alissa do not appear to have prevented him from getting into the university spirit - sniffing out other opportunities. So the Tommy/Alissa storyline is left unresolved - a pity really because they were, in many ways one of those cute couples you only get on TV.