TV tonight: oceanic wonder with David Attenborough in Blue Planet III

8pm, BBC One
Life is every bit as strange and beautiful at the bottom of the ocean as it is on land – and it is even more profuse. In his 101st year, David Attenborough is still finding amazing things to show us. The quality of footage the BBC Natural History Unit now records is truly startling. The return of this beloved series begins in tropical seas where constant sunlight stimulates an extraordinary range of life. Look out for the remarkable team-hunting strategies of the tawny nurse sharks, as well as an incredible tussle between a pair of shrimps and a starfish that culminates in the shrimp stealing and eating the starfish’s arm (don’t worry, it grows back). Consistently amazing. Phil Harrison

BBC Young Musician: The Final

7pm, BBC Two
Violinist Sofia Demetriades, saxophonist Kezia Colton and recorder player Alma Nunez Debretzeni are the three contenders as Petroc Trelawny hosts the climax of the search for the next Nicola Benedetti or Sheku Kanneh-Mason. In the auditorium at Bristol Beacon, the remaining trio must decide: push for that little bit of extra magic in their performance or focus on technical perfection? Jack Seale

This City Is Ours

9pm, BBC One
How far is Michael willing to go to protect Diana? As the third episode of this tense crime drama begins, Michael faces an ultimatum with terrifying ramifications. Elsewhere, the problems are mounting for the Phelans as they search for Banksey. It’s gripping stuff, underpinned by a lead performance of restrained menace by James Nelson-Joyce. PH

Mortimer & Whitehouse: Gone Fishing

9pm, BBC Two
Living the bream: we’re now in season nine but Bob and Paul’s elegiac riverbank escapades still charm and amuse. This time, there’s a touching Ted tribute which is undermined somewhat by Bob wondering if the deceased dog will “go up or down”. Then, to some fishing: but will Norfolk’s rivers surrender their bounty? PH

Adultery

9pm, ITV1

An illicit weekend away in the Lakes is never going to end well, is it? But that’s the stage Beth (Romola Garai) and Tom (Dominic Cooper) are at with their affair. At home, their kids – who are also dating each other – are also hitting some hurdles. What a mess. Hollie Richardson

Bradley Walsh’s Million Pound Shot

9pm, Channel 4
A Bradley Walsh gameshow seems an odd choice for Sunday primetime. In fact, based on the track record of the production company and the lack of information, speculation is mounting that trickery is afoot. For the record, we’re promised a “quiz event” with a million bucks on the line. We might get something else entirely so it’s surely worth tuning in to find out? PH

Live sport

Women’s Super League Football: Charlton v Chelsea, 2.15pm, BBC Two At The Valley.

Premier League Football: Liverpool v Arsenal, 3pm, Sky Sports Main Event Newcastle v Everton is on Mon at 6.30pm.