Ben Wheatley's first two films—the gangster flick Down Terrace and the occult hit-man horror film Kill List—are marked by tendencies to genre hop in ways both stimulating and dumbfounding, mainly in the punctuation of surreal comedy with disturbing violence. Both films are often brilliant but ultimately frustrating, mainly because they don't pass the true genre test: Would Kill List still be engaging if the characters weren't hit men? Would Down Terrace still be effective were it simply a family drama absent of criminality? Divorce either film from its genre, and does it still work? 

Sightseers could have been a cheeky British take on Natural Born Killers, with its story of a murderous couple's road trip across the countryside. Yet there's an undeniable sweetness to the film and its core players, two thirtysomething oddballs on a tour that includes stops at museums dedicated to trams and pencils. It's a caravanning dream trip for the frumpy and overly gregarious Chris (Steve Oram), whose planned "erotic odyssey" with new flame Tina (Alice Lowe)—a lonely dog psychologist who spends her time crocheting crotchless panties—takes a very dark turn following an encounter with a litterbug. That incident launches a series of increasingly gruesome encounters as the pair hops between RV parks and leaves a trail of bodies behind. All the while, Chris pretends to write a book and Tina follows him like a sad puppy, making seriously misguided attempts to win his affections.

Wheatley shows off his gift for the bizarre, jackknifing the film between boring tourist traps and hallucinogenic nightmares, but Sightseers belongs to Lowe and Oram. The pair, who conceived Tina and Chris seven years before filming, have an easy rapport, and their conversations, bickering and affection—largely improvised—make them exceedingly pleasant cinematic companions. It becomes easy to forgive their crimes, which are almost afterthoughts.

That's what makes Sightseers so challenging, and yet so strangely watchable. It's a film about characters on what some might consider the most boring vacation possible (with respect to the Pencil Museum), but it works because its characters are so well-drawn. At no point do we leave the pair's side, and as a result, we're both implicated in their actions and horrified by them. But remove the murders, and Wheatley's film would still stand as a quirky portrait of the blossoming and flawed love between two lost souls. That they remain sympathetic as they wash blood from their hands is a feat unto itself.

Critic's Grade: B+

SEE IT: Sightseers opens Friday, June 7, at Living Room Theaters.