Justin and Riley's relationship is put to the test after a spontaneous wedding goes awry and Billie makes a daring decision that could risk a prestigious internship that awaits her in the city. Meanwhile, Maisy reckons with life-changing news about an old enemy: her mother, Mimsy.

An opportunity arises for Justin to redeem himself when he discovers the Boathouse fire may have been the result of foul play. Meanwhile, Billie's eco-ideals are challenged by a magnetic nemesis and Maisy tries to prove her mother is lying about her imminent passing.

Justin makes a deal to obtain evidence that could prove his arson theory while Billie struggles to adapt to the harsh physical demands of tree planting. Meanwhile, Maisy attempts to draw out her mother's lies with a boring AGM, but nothing seems to crack Mimsy's veneer.

Justin crashes Jayne's Aqua Spin class to interrogate arson suspects. Billie is torn between her personal and professional life, and Maisy uses a "spa day" to extract medical samples from Mimsy.

Maisy uses the anniversary of Derrick's passing to get Mimsy to confess to burning down the Boathouse with Justin's help. Desperate for any opportunity to avoid her sibling love triangle, Billie agrees to go to Derrick's anniversary dinner in exchange for Justin promising to get her a job from Maisy.

When Billie's two crushes show up at the cuddle cabin, she enlists Justin in a game of keep-away that ends with a broken heart. Meanwhile, Maisy plans a celebrity soirée for cottagers to remind them why they need a Boathouse.

When her parents come for a visit, Billie has to make good on her lie that she's been giving tours for the lake for her summer job. Justin and Riley pose as a happy couple to secure a property for the Boathouse rebuild while Maisy struggles to deal with the reality of her mother's illness.

Justin and Billie trap all the suspects on a pontoon boat to clear his name by exposing the identity of the Boathouse arsonist. Keen to get to the tree planter's farewell party before Ivy and Forrest leave, Billie agrees to help Justin. Maisy finally accepts her mother's diganosis and decides to make peace before the summer ends.