The Murder Detectives (Channel 4, 9pm)

REALITY TV takes one of its biggest leaps into the unknown by spending three nights showing the hunt for clues when someone is murdered.

Every twist and turn of a police investigation into the horrific killing of a teenager is part of the The Films of Record series, directed by Bafta-winning director David Nath (of Bedlam fame), filmed over 18 eighteen months with intimate and unprecedented access to a police major crime unit in Bristol as they investigate the stabbing of a 19-year-old.

Those of us who enjoying guessing the murderer from TV drama clues, and there are too many to mention, will be able to follow the drama in real time and catch of glimpse of how detectives' minds are working.

Of course, there is also the heart-wrenching story of a young man’s senseless death, his family’s pain and the polices’ determination to achieve justice for them at its.

We see three different worlds: a detective faced with an apparently motive-less crime, a family desperate for justice and another who’ll do anything to save their son from a life behind bars. We are taken into a world of knives and disrespect – the currency of the street. We’re led into a world of bad choices and moral dilemmas and as the net closes in we begin to see the ripples that spill out when a murder is committed.

Nath says: "This is the story of a senseless stabbing, a young life cut short. In Britain, it’s a story of now. If this series makes even one kid think twice about carrying a knife, then it will have been worthwhile. The impact of murder on a victim's family is absolutely horrific and we are immensely grateful to them for allowing us access."

The clock starts tonight from March 5, 2014 when Nicholas Robinson has his life cut short. His desperate last breaths are heard as he makes a 999 call before collapsing and dying from multiple stab wounds. Nicholas was studying at college and had recently got engaged to his long-term girlfriend. The police had only had contact him when he reported his bike stolen two years previously. A single black glove found at the crime scene could provide the answer.

We don't glamorous detectives laying down the law and breaking the rules to gain a conviction, no matter the cost. Instead, it paints a true picture of what happens when somebody loses their life at the hands of another, and the actions of the police team charged with bringing the killer to justice.

Amid it all are Nicholas's devastated parents – he is the second child his mother has lost, while his father tries to channel his grief into getting justice.

The World's Most Famous Train (Channel 4, 8pm)

WITH the price of a ticket set at £2,000 for a train journey that takes 36 hours and boasts neither wi-fi nor showers, there is still bound to be plenty of interest in the romance of the Venice Simplon-Orient-Express.

According to Agatha Christie, some people have found it murder to stay on board, but the rest of us can dream about joining the elite on the rails... even if the final destination of Turkey has lost a little of its allure.

During its nine-month-long season, the express makes more than 60 journeys, covering 150,000 kilometres, with the majority of trips between London and Venice. The train is comprised of 17 unique 1920s carriages and we follow the stories of the staff and passengers as the train makes its way across Europe.

London Spy (BBC2, 9pm)

DANNY is confronted with a side of Alex's life that seems to undermine the very foundation of their relationship. As he wonders whether to give up his private investigation into his lover's gruesome death, he realises a vital clue has been overlooked. Tom Rob Smith's thriller, starring Ben Whishaw, Edward Holcroft and Jim Broadbent, with Adrian Lester, Harriet Walter and Samantha Spiro.

Viv Hardwick