Donna Martin (Tori Spelling) returns for a surprise visit at Kelly and Silver's place. Donna's visit is more than social, agreeing to create a dress for Oscar-winning Juno screenwriter Diablo Cody. Meanwhile, Annie joins her brother on his search to find his real mom, and Naomi and Liam volunteer for Habitat for Humanity. Dixon convinces Annie to search for his mom in Arizona. Ryan urges his students to sign up for Habitat for Humanity. Ethan signs up as well as Naomi, who etches at the opportunity to work alongside her crush Liam.
Kelly, poised to give Silver the "mood chart" test, frustrates Silver who is fed up with Kelly's exhausting tendencies. Donna, a prominent designer in Japan, has returned to the 90210 with her daughter Ruby to say hi to her half-sister-in-law. Just as Silver is about to be told of Donna's adventures overseas, Kelly interrupts, saying it's bedtime.
Donna and Kelly take a drive through the old 90210, and Kelly asks about David. It is obvious that Donna is hiding the true reality of the situation, and big trouble awaits for Donna in Japan. At lunch, Diablo Cody comes over to Donna and compliments her on her dress. Donna then agrees to design a dress and style Diablo.
Silver is envious that Donna met her idol Diablo and Donna asks Silver to help her with the dress, but Kelly refuses. Silver is upset and not even Donna can smooth out the tension between the two,
At the premiere party, Diablo runs out onto the red carpet with Donna still working on the dress. Kelly and Silver watch this on the television and both find the unforeseen event hilarious. They ultimately come to a middle ground on Kelly's rules; however, Silver's prayers are answered when Donna brings Diablo back to meet her.Later that night, Donna reveals over tea that she and David are separated.
Annie and Dixon drive on the open road to visit water parks, but the whole trip is a lie. Not only do Annie and Dixon's parents believe they are going to Palm Springs, but Dixon hasn't told Annie that they are in Arizona to find his real mom. When he tells Annie the truth, Dixon reveals he the options he was given at age 8: be put up for adoption or stay with his mother. He adoption because he was so angry at his "crazy" mom. Now, he wants to be at piece with himself and apologize to his mom.
Annie and Dixon find his mom, but when Dixon freezes when he sees her eating lunch outside the house. Annie decides to approach her and introduce herself as Dixon's sister. She apologizes for Dixon, saying the experience was more than he bargained for. She invites Annie to sit with her and share childhood stories of her son.
At the Habitat for Humanity site, Naomi cannot read Liam's feelings for her. So she asks her ex Ethan to find out how Liam really feels. The two boys don't get along, and nothing is settled until Liam grabs Naomi and kisses her. Later, Ethan becomes high off of Liam's concoction and reveals that he's sick of being the good guy while Liam guides him through the woods.
Liam falls and hurts his ankle. He admits that Ethan is not high but feeling the effects of herbal tea, just to mess with him. After helping him stand up, Ethan knocks Liam for being a jerk. Liam tells Ethan hallucinogens aren't what they seem and tells of how he almost cut off his arm after taking acid. And by the end, the two become friends.