Living in a boat on the canals of London, Eva and Kat (Chaplin and Tena) are a loved-up couple. They occasionally drop in on Eva's quirky mother (Geraldine Chaplin), which makes them a little crazy. Then Kat's lively friend Roger (Verdaguer) arrives from Spain for a visit. One drunken evening they hatch an idea for Roger to father a child with Eva. In the morning, they need to work out the logistics, which are complicated by their emotional connections. Eva is still super-keen, and Roger is up for it too. But Kat has doubts.

Much of the film consists of conversations that have a refreshingly improvisational feel, as these three people speak at the same time, joking around even as they discuss important issues. The interaction between Eva, Kat and Roger is playful and meandering, veering easily from silly to serious. With lovely cinematography by Dagmar Weaver-Madsen, Marques-Marcet cleverly uses the settings to isolate this trio in the narrowboat and on towpaths. Even when they are walking or running in silence, they are communicating.

Chaplin is terrific as a young woman who begins to realise how badly she wants a child. Her connection with Tena is powerful, and Tena brings out Kat's complex mix of spiky stubbornness, earnest questioning and deep affection. As the third wheel, Verdaguer is funny and charming, constantly provoking Eva and Kat to think in new directions while indulging in his own man-child irresponsibility (plus rocking some ridiculous facial hair). As a result, his own quietly thoughtful moments are surprisingly strong.

There are times when the plot seems to move as slowly as the boat drifts down the canals; some judicial editing might have spiced up the pace. But as it is, the film is nicely observational, cutting through the surface to touch on darker underlying feelings. And as the story develops, it says some profound things about the give and take required in any relationship, the difficulties of growing up and the need to move forward. So where each of these characters goes is engaging.

Sketch artist Cole (Cabral) travels west to escape his dead-end life and a bad break-up in New York. He stays with his best friend Daren (Brown), who has just had a big promotion at work and announced his engagement to Rebecca (Liu). Her sister Charlie (Elizabeth) lives with them as she gets her life back on track. Then just as Cole decides to stay here permanently, he runs into the ex (Lee) he's still pining after. He also begins to realise that his drawings are predicting the future. But trying to make things happen isn't as easy as it should be.

Both Daren and Cole need someone to talk to as they work out the next step to take in their lives, grappling with secrets they feel they can't share with anyone else. Daren confesses that he never intended to get engaged, while Cole struggles with finding work and making sense of what Daren calls his superpower. Instead of focussing on the magical realism angle, the series centres on their friendships, which play a key role in helping them decide what to do with their lives.

The cast is nicely understated, never over-egging the subtle melodrama in the plot. Each of the four central characters has a strongly distinct personality that's easy to identify with. They're young and hot, and also likeable and complex, a cool mix of serious drama and warm comedy. Both Cabral and Brown give enjoyably layered performances, offering surprising textures as they interact with both the main supporting cast and a range of smaller characters who have an impact on their journeys.

This magical sketchbook offers an inventive exploration of the idea that we make our own fate, that intention is the key to moving forward. As Cole tries to use his drawings to actually change his luck, the series thankfully avoids both trite plot twists and wacky slapstick. Instead, it focusses on the personal connections between the characters, including a wide variety of relationships from warm and supportive to suggestively romantic. And while the final episodes get a bit more plot-based, they remain thoughtful and pointed.

Lisa and Dan (Karpluk and Edwards) are looking forward to a weekend in a gorgeous lakehouse with their friends Skai and Teejay (Agostino and Xavier). Unknown to Lisa, Dan has also invited Fiona and Geoff (Kirshner and Chernick), which complicates their plan for a bit of partner-swapping. Especially since Fiona had no idea what the plan was. With tension in the air, they set some rules and get on with it. But of course nothing goes the way they expected it to, and each person is going to need to accept a new reality.

The film bristles with awkward humour. Lisa and Dan are simply trying to spark their tired marriage with a no-strings encounter. Fiona feels ambushed. The sexy Teejay and Skai seem like they're a little too keen (they're also the only vaguely mature people in the house). Their encounters initially play for comedy value, avoiding anything remotely sexy or complicated. There's much talk about the struggle to maintain a long-term romance, which reveals the filmmakers' preachy intentions. But darker discussions are far more interesting.

Each actor brings offhanded charm to his or her character, making them easy to like even if they never seem realistic. All are smart, fit and open-minded, so why have they failed to openly speak with their partners about relationships or sex? Karpluk and Chernick have a nice heart-to-heart about how difficult it is to sustain sexual interest after years of marriage, careers and children. Edwards has fun as Dan, who falls like a hapless schoolboy for Agostino's Skai. And each actor plays scenes of conflict with real force.

One rule for this weekend is that the partner-swapping doesn't mean anything. So the script avoids the topic while making mountains out of the resulting molehills. This assumption of morality simplifies everything as each relationship is pushed to a breaking point. Thankfully, things deepen in intriguing directions that highlight a variety of big issues. There's superb dialog between the characters, and the actors dive in with charm, energy and passion. Perhaps if the filmmakers and actors weren't so timid about sex, the film might have had a stronger kick.

In his caravan on the Isle of Sheppey, David (Hoyle) is entertaining Michelle (Redford), his young cross-dressing paperboy, who's clearly wants something from this encounter. As they talk about things like why children should be watching Pasolini's Salo instead of going to school to learn how to shop, they notice beardy he-man Matt (Daniels) in a nearby house. David flirts aloofly, but Michelle goes in for the kill. Meanwhile, Matt's sister (McCormick) is intrigued by these two neighbours. She has been talking to David, and when Michelle invites her in, events take a surprising turn.

While the film is meandering and awkward, with conversations that somehow feel both scripted and improvised, there's an underlying method to Hoyle's madness. This is a bracing assault on the fake surfaces that define civilisation, from the makeup women feel they need to wear to clothing, music, sexuality and breathing itself. All from the perspective of this beach on the edge of the world. The movie's primal undercurrents are sometimes overwhelming, catching us off guard as they emerge from skilfully askance angles.

Hoyle's performance is majestically godlike, a middle-aged man who astutely observes the world and makes fatalistic decisions. He aches for a sense of belonging, a lover to share life with, but no one he meets is quite up to par. The three actors around him are less arch, more naturalistic as they play variations on archetypes: the young nymph, lost lover, insecure tough guy. All three are magnetic enough to catch David's attention (and ours too), even if they are doomed to let him down.

Where this goes is artful and challenging, pushing the boundaries of what movies are expected to do. This certainly is not a standard narrative feature; it's a performance piece playing with enormous issues in ways that are hilarious, unsettling and shocking, often all at the same time. This kind of singular work comes with both a high recommendation and a note of caution. But it's a movie that can jolt us from our view of comfortable society. And the climax leaves Hoyle free to indulge in his imagination for another chapter in this story.