Cert 15 98mins Stars 3

This diverting thriller is a dramatic change of scene for Claire Foy.

The Brit actress swaps the intense goldfish bowl of royal family life on TV’s The Crown for a stretch as an inmate in a psychiatric asylum. 

Well at least I think there’s considerable difference between the two institutions.

Foy’s tremendous as a victim of stalking who unwittingly commits herself to observation in a secure facility, and is unable to persuade anyone of her sanity.

An early convert to digital photography, director Steven Soderbergh follows the example of 2015’s art house hit, Tangerine, by shooting shot Unsane on an iPhone. 

And this has a juicy opening as Soderbergh mixes in elements of medical corporate conspiracy from his previous films such as 2013’s Side Effects, but he soon back pedals into well executed but predictable slasher territory. 

His use of wide angled lens emphasises Foy’s isolation and anxiety, but this decent stab at claustrophobic paranoia is never sufficiently barking mad.