SPOILERS UP TO EP 7. I've tried to watch back to pick out major events relating to each of the characters:

Claire

• was very close to Pippa (who wanted to be a hairdresser when she grew up ep 5), gave her a precious pendant that belonged to her grandmother
• was interested in Ellie’s kid, went quiet when she was asked if she had any (ep 1)
• did Cate’s hair before the wedding at 4pm
• claims she went over to a friend’s came back and had a drink with Lee only to be drugged
• slapped someone asking “what have you done?!”
• had an abortion while Lee was arrested
• stole pendant from detectives
• got sent a bluebell
• repeatedly says she does not want to be back with Lee again, but she can’t help herself
• was in contact with Ricky and Lee, googling Lee pendant/trial/guilty
• angry at Lee’s accusation "after all she’s done for him” (ep 7)
• tells Paul she’s out of places to run
• returns pendant (why now? maybe because she doesn't want to protect Lee anymore)

Lee

• close to Pippa (she liked to go see him), his hair was found on her pillow and her pendant in his car (which he sold)
• very close with Lisa (knew about Thorpe from her?), lied about his relationship with her and went quiet when Hardy asked if he slept with her
• installed a gate between Gillespies and their house for the Ashworths to go over easily
• slept with Cate presumably in one flashback scene, Pippa almost found out (Claire was unhappy with their relationship)
• did church flooring in the morning the day of the murder, captured by CCTV at 4.47pm while buying stock
• then he did floors for his own house while Claire was doing Cate’s hair
• photo shows Claire, Lee, and Pippa with some loose floor boards taken 1 week before so it was planned
• Claire claims he was cleaning the house and the floors the night of murder
• went to France after trial collapsed, now wants his old life with Claire back
• persuaded Hardy to reopen the case (if he was guilty, why would he do this? then again he might want to drag other people with secrets down with him a la Joe Miller)
• violent with Claire include trying to strangle her (ep 6) and drown her (ep 7)
• also seems to have visited the furnace at some point in time
• says there is “almost nobody” who know him in France

Ricky

• made a pass at Lisa
• finished work at 4.45pm before wedding
• was at wedding but disappeared after bridesmaid rejected him
• in possession of Rohypnol drug
• told off Hardy, but apologised and expressed he did not want the case reopened (why, if he was innocent?)
• asked to meet Lee
• lied about his location during the wedding and about Thorpe

Lisa

• bad relationship with father (Ricky’s brother), "uses" mother’s surname
• told Claire that she hates Cate (while Lee was flirting with Cate)/ Pippa?
• 3.54pm bank account was last used
• 5.17pm called her mother
• last signal in Portsmouth, ferry to France?

Thorpe

• stalks Lisa
• owns an incinerator
• RSVP to wedding but did not turn up
• tried to kill himself night of murder
• Ricky knows him through Lisa

THING OF NOTE: Remember how during the opening scene of Broadchurch 1, Joe's character was directed to play-strangle Tom? I think this series the parallels might be during the woozy flashback scenes with Lisa and Pippa. During the flashbacks, Lisa holds a finger to Pippa telling her to be quiet (ep 1). During another scene (I think ep 5/6?) Lisa is running to Lee while he holds a finger up to Pippa, and Lisa hides behind a tree while Ricky appears behind Lee saying "gotcha!".

My theory: Lisa is in love with Lee, decides to run away with him to France. (She breaks up with Thorpe causing him to want to kill himself.) She withdraws the money for the trip, but gets her plan exposed by Pippa. Lisa threatens Pippa not to say anything to Ricky or her father but accidentally kills her. She runs to Lee for help, who tells her to go on the run. Lee hides Pippa's body in the floorboards. At this point, he either (1) drugs Claire until he can transport Pippa's body to the woods, or (2) gets Claire to get rid of the body while he cleans the house. Claire realises what happens, slaps Lee, because she was very attached to the girl. Lee sells his car to avoid suspicion, not knowing her pendant drops in the car. Claire steals the pendant evidence back because she can't bear to see him go to prison for something he did not do. I'm guessing Ricky knows what happened (maybe Pippa got a message out to him before Lisa killed her, or he was out after the wedding and saw Lee's car near the woods) and that's why he sent a bluebell to Claire.

What does everyone think? Is Ricky more involved? Why was Lee using the furnace? (to fake Lisa's death?)