In "Welcome to the Black Dog House," summer has officially arrived on the island. Katie arrives on the Vineyard at a crossroads, in both her career and her relationship, while Emily is determined to find her very own "JFK Jr." Jackie has returned to the island to be closer to her mom, but once she meets Luis she quickly realized this summer will be filled with interesting possibilities. Ben confides in Cat about the real reason he's come home, but will she keep his secret? Meanwhile, the tension between Jon and Luis finally erupts at the welcome bonfire when they come to blows over Katie.
Jonathan steps up his pursuit of Katie, much to Lou's chagrin; Lou kisses Katie's friend, igniting jealousy in Katie.
Jackie is crushed when she learns Luis may have feelings for Katie; Cat warns Sophi to stay away from Ben; Sophi works up the courage to sing in public; two housemates try to keep their budding romance a secret.
Katie deals with the fallout from her beach sleepover with Lou.
A heartbroken Lou decides to leave the island instead of facing Katie.
Daniel hosts a rooftop party, which he hopes will spotlight Sophi's talent; Katie is pleased when Luis returns to the island, but Cat fears that Katie will cause him heartache; and Jon attempts to win back Emily.
The biggest secret of the summer finds its way to Katie.
The Black Dog crew looks to the future as summer comes to a close; Cat must choose between romance or her career; Jon and Emily ponder their relationship; Luis makes a romatic gesture to Katie.