Lydia Sparks is a ditzy young woman who is heavily pregnant when she is befriended by Angela. It is soon revealed that the child she is carrying is either Tommy's or Angela's ex-husband Frank's. Eventually the child is known as TJ, for Tommy, Jr., once a test confirms that Tommy is the father.
Tommy had introduced Frank to his old girlfriend, Lydia, who then endeded up as Frank's girlfriend and fiancée.
Lydia introduces her Fiancé, Stuart "Strawberry" Strawbridge at Tommy Jr's Baptism. They plan to move to Abilene and Strawberry wants to have his "own kids". This will be possible because Tommy Sr didn't turn in his custody paperwork. The Rizzolis hatch a plan to get Lydia and Tommy back together.
Jane and Maura host a girls night with Lydia and when Tommy shows up on the pretense of moving a couch Jane ruins dinner and drags Maura out for takeout. Tommy and Lydia fight and Lydia storms out. Maura says they should "get rid" of Strawberry. Jane admits she ran his name and he has no record. Maura says that Stuart has severe allergies. Maura and Jane are going to babysit T.J. while Lydia and Stuart go to a going away party and Tommy comes in with Jane's dog, Joe Friday. It turns out that Stuart is severely allergic to dogs, which ruins Lydia's fantasies of a house full of kids and dogs. Stuart leaves and Lydia and Tommy goes for a walk.