Bradford theatre company Lost Dog comes to the South London arches (vaulted, not proscenium) with its two-and-a-half-man gentle reflection on the complexities of love. Claire (Sally Cairn, pictured) is a coy, hands-in-sleeves editor of children’s books. Paul (Rich Warburton, a bulky Paul Bettany) is affable, effortful, and a little jumpy. Very jumpy, in fact.

Paul has some manifestation of Obsessive Compulsive Disorder. A cartoonist (actually, he just does the colouring and he’s a temp), he talks to ‘himself’ in the mirror (in the second person), folds his jacket according to a well-drilled routine, and always sets his pencils out the same way: parallel to one another and exactly perpendicular to the desktop.

Paul, we discover as the storyline flashes back and forth, is also the kind of chap who invites a co-worker to his office to watch a neighbouring Post Office being demolished. And who, on their first date, witlessly takes Claire to a pornographic art show. And so we find them, sitting in a café afterwards, struggling through excruciating small talk about the cleanliness of the loos. Luckily for Paul, Claire is a forgiving soul: “He’s not weird – he’s quirky.”

The Southwark Playhouse is a good venue for that hear-a-pin-drop atmosphere, but Cairn and Warburton work up a real sympathy – frequently amused, if tinged with a vague regret for things not yet past – for their hopelessly mismatched pair, as they try to navigate through the minefield at the centre of every relationship: namely, the frustrations (practical and emotional) of fitting in with other people’s rules, formulas and habits.

Cairn’s cute Scottish accent strikes just the right balance of optimism and unhappiness, and both actors achieve a small dramatic feat every time they have to cut from domestic anger to nervous coffee shop chit-chat.

The disjuncture is well worked, as is the slow, irregular transition to some kind of stable happiness, Claire and Paul beginning, as one song narrates, to fit into each other’s “patterns”. (James Dey performs his newly-commissioned soundtrack live on stage. It’s slightly James Bluntish – that’s not rhyming slang – but his presence is purposeful, we discover later.) Love in (3) Parts (brackets never explained, though I wondered if it might be some form of labial emoticon) is “devised by the company” – which always sounds like a Mafia hit (“Harold Pinter’s The Caretaker: being taken care of by The Company”) – and for the most part it’s spot on, though one random moment of dance sticks out oddly in its isolation. Still, as Claire avers: “Nothing’s perfect. Isn’t that why we have editors?” Hm. Well, she would think that, wouldn’t she?

Southwark Playhouse, until January 31. Tickets: £8 - £18, 0207 407 0234 (