Exile
BBC1: 4/5

Case Sensitive
ITV1: 3/5

Sunday evenings have a reputation for being depressing - around 8pm as the gloom sets in and the credits roll on Antiques Roadshow is the time when you are statistically most likely to considering ending it all (or is it just me?). Throw a BBC drama about an Alzheimer's victim into the mix and one imagines that the nation would be queuing up for a prescription of Prozac.

However, Exile, shown on successive nights this week starting from Sunday, proved the perfect antidote to those royal wedding withdrawal symptoms. As a portrayal of Alzheimer's it was touching and believable, but this was more than just worthy social drama. It was also a truly exciting, edge-of-the-seat thriller which managed to avoid nearly all of the clichés of the genre through some brilliant writing and wonderful performances, notably by Jim Broadbent as Sam, a retired journalist, crippled by dementia.

I say nearly all. Sam's son, Tom (John Simm) was the cynical, hard-drinking investigative-journalist-in a-mid-life-crisis that you tend to find in many thrillers. Having lost his job on a lads' mag after sleeping with the boss's wife, Tom returned home to Lancashire to confront his troubled past. His father was now too confused to speak sensibly and his sister Nancy, Sam's carer, was not prepared to delve into uncomfortable memories. But Tom - being a cynical investigative journalist - managed to uncover that at the root of all his problems was a corrupt local council leader called Metzler. The breathless plot managed to encompass Tom's affair with a married woman, Mandy (Claire Goose), and the discovery that he had been adopted. But the story never neglected the poignant central relationship - the best treatment of a neurological disability since Tom Cruise teamed up with Dustin Hoffman in Rain Man. The observation of Alzheimer's by writer Danny Brocklehurst was clearly well-researched. The confusion, disorientation and blackest of black comedy was interspersed with enough moments of clarity to move the plot along and bring Exile to life. Broadbent will no doubt pay him tribute when he picks up his Bafta.

Over on ITV, there was Case Sensitive, another psychological thriller which, while less inventive, had the virtue of a labyrinthine whodunit plot and high production values, and made up in beautiful camera work what it lacked in inspiration.

At its heart was that favourite of psychological thrillers, the stalker - this one a warped criminologist hunted down by DS Charlie Zailer (Olivia Williams) and DC Simon Waterhouse (Darren Boyd).

The pair are called in to investigate the death of a mother and daughter at their minimalist glass-and-concrete futuristic home. There was a moment when, as the camera panned around the living room, it seemed that we had strayed into Location, Location, Location territory, but with no sign of Kirstie Allsop.

The tense denouement took place in a deserted, boarded-up house - expect the property to make a return to your TV screen soon in Homes Under The Hammer.