DVD REVIEW: Your Sister’s Sister, (15), (90 mins), new on DVD.

It’s the weirdest thing. Give actors lines to learn and they will sound as if the lines are pouring from their hearts.

Let them improvise, and you’re soon listening to conversations no one on earth will ever have, mired in all sorts of forced phatic utterances which have all the life of a dead badger.

And so it is with Your Sister’s Sister, a film which makes nits of pretty much everyone concerned – though in its final half-hour it does get into its stride to a certain limited extent.

It’s a shame because at heart there’s a nice if-not-exactly-everyday dilemma running through it.

Jack (Mark Duplass) is like a bull in a china shop since the death of his brother who used to be the boyfriend of Iris (Emily Blunt) who is now, slightly bizarrely, his ie Jack’s best mate.

In fact, they are deeply in love if only they would realise it and their best chance of happiness is just there for the taking if only they could see what is staring them in the face.

Enter the complication. Iris packs Jack off to her parents’ retreat to have some Jack-time, not realising that her older, lesbian sister Hannah (Rosemarie DeWitt) is there having some Hannah-time having just broken up with her lady friend.

After a few drinks, the pair hop into bed, only to be woken from their sexual exertions the next morning by the unexpected arrival of Iris.

So… after one night of passion, Jack now risks losing Iris forever, as does Hannah; and if that’s not bad enough, Jack soon discovers that Hannah may well have been using him from the start.

All the ingredients are there for the mother of all bust-ups; but the trouble is that woeful, oh so awful dialogue, punctured at every turn by errant umms and ahhs and three actors with all the on-screen naturalness of a stripy pink dodo.

They might as well have “hmmm, what would my character be saying now?” plastered across their foreheads.

Give the poor blighters a script and we might have got somewhere. As it is, we harrumph, strop and meander towards a sudden finish which is either rather clever or else a total cop-out. Probably the former.

Phil Hewitt