Best friends Libby and Jess from Southampton want to arrange an unforgettable 18th birthday party for identical twins Holly and Charlotte who are Libby's younger sisters. Despite having already turned 18, the pandemic meant the twins never got to celebrate in the proper style, so the girls are hoping the Big proud Party Agency can put things right.After hearing what the girls have to say, the party agents compete to win the business. Ryan pitches a VIP glam-up disco with high-fashion style and paparazzi. Christopher whets the appetite with a pool party featuring some half-naked "Mermen" and Teddy wants to set sail on a superyacht before ending the night in a super club.After Libby and Jess choose their favourite party idea it's time to get down to business. The winning party agent, supported by the others, heads to Southampton to put their plan into action. The décor has to be hand-picked to suit the theme, performers are auditioned for their very specific talents and a dance routine is lined up as an extra special surprise. Will the twins get the 18th Birthday Party they always wanted?