The Sea Keepers are invited by Queen Adrianna to stay overnight at the palace for Princess Marina's surprise birthday party. Emily, Grace and Layla have never been to a mermaid sleepover, and are worried about what gift to bring. But when Effluvia crashes the party and threatens to spoil the surprise, Emily, Grace and Layla know that they need to give their mermaid friend the only birthday gift that really matters - a magic pearl that can save Atlantis from evil Effluvia! They won't sleep a wink until they find it!