Here's what I pieced together after seeing these and the released titles.
Seeing how Tom seems to be wearing a seashell necklace in the op image it most likely takes place after the beqch episode which is probably Swim Suit.
So it's either Ransogram or Lava House Fever. Most Likely Lale House Gever and this >>105850892
being the titular lake house
Ransogram will likely be a solo Marco episode judging by >>105860098
So it's likely that Ransogram and Lake House Fever are another pair of episodes that happen simultaneously. Which would explain why Marco isn't in the pics of the Diaz house, he's off being Mad Marco.
My theory is that the image in the op is Tom walking in on Star giving Marco a goodbye kiss which is why he's shocked and proceeds to try and burn down the Diaz house. Up to this point Star probably hasn't officially broken up with Tom yet but has all but gotten together with Marco. The writing is on the wall for Tom and Stars relationship but they haven't addressed it yet and maybe Tom thought this meant he still had a chance with her. So he runs away to hole up in his lake house but Star chase him there to properly end things while Marco is off doing adult stuff in his adult body
Lake House Fever is the Star and Tom break up episode and Starco happens either in Swim Suit or before.