Helped by the sole writer on this series, Roger Marshall, there’s a strong sense of continuity between the stories – so that at times it feels more like a serial than a series.  This is evident in Case for the Defence, which harks back to events and characters first seen in Paid in Full.

During Paid in Full, Marker tangled with Detective Constable Broome (Leslie Lawton) who was convinced that Frank had stolen a colleague’s pay-packet.  Eventually the true culprit is caught and Broome returns here to try and make amends for the injustice Frank suffered (losing his job at the builder’s yard).

Frank’s now got another job, stacking supermarket shelves, but it’s obviously far from satisfying.  Broome tells him that there’s a position vacant at a local detective agency.  It’s a tempting possibility – although it would mean the fiercely independent Frank would have to work with others (which isn’t always his strongest point).  But the chance of returning to what he knows best is irresistible, so he accepts the offer of the agency’s owner, Joe Rylands (Stanley Meadows).

His first case involves gathering evidence for the defence concerning the forthcoming trial of Barry Osborne (Billy Harmon).  This is another link back to Paid in Full – as Marker encountered Billy during that story at the police station (Marker was in another interview room, discussing the wages theft).  It’s an undisputed fact that Billy killed a garage owner, Flockton, by stabbing him with a screwdriver.  There seems to be no reason for this, which is even more baffling when you consider that Billy comes from a wealthy family and has received every privilege.

His father, Ben Osborne (William Lucas), is keen to impress on Marker that he wants his son to get off, by whatever means possible.  It’s a powerful performance from Lucas, portraying a single-minded wealthy man (who’s made his money by being the main meat supplier for the county) used to buying whatever or whoever he wants.  This is going to place him on an inevitable collision course with Marker, who prizes the truth highly and will refuse to be cowed or intimidated by him.

Frank is able to establish that Flockton had gone to prison a decade earlier for GBH.  Osborne is delighted – it gives them a chance to craft a plea of self defence.  Together, Osborne and Frank visit Flockton’s victim, Mr Jackson (Richard Bird). but a series of strokes has rendered him virtually unintelligible.  Osborne’s pressurising of the sick old man disgusts Frank, who exits the house.

By now, Frank’s seen more than enough to be convinced that Osborne will do anything, including bribery, to ensure that he can produce witnesses to support his line of defence (that Barry was attacked by Flockton and inadvertently caused his death whilst defending himself).  Frank corners Rylands and lets him know what’s been going on.

MARKER: I think you ought to know that you could be letting yourself in for a great deal of trouble.
RYLANDS: How?
MARKER: Friend Osborne and his cheque book is going around getting at witnessess. Bribing them, getting them to perjure themselves.
RYLANDS: Strong words.
MARKER: Well you’d better hear them now than in the dock.
RYLANDS: Any proof?
MARKER: Not yet.
RYLANDS: Well I’m glad you let me in on this, Marker. Yes, they’re very pleased with you, you know. I’m delighted.
MARKER: Well I don’t want another job to fold up underneath me.
RYLANDS: You’re quite right. But you must remember Marker, when you’re paid to turn up stones, you mustn’t get too queasy at what you find underneath.
MARKER: I’m not queasy, but I just don’t want to be there when he offers the judge fifty quid and a years free meat.

In the end, Barry decides to plead guilty, despite his father’s protestations.  Exactly what happened at the garage is never established, and never will be.  It’s possible that Barry was defending himself, but equally it could just have been a motiveless murder.  Later in the story, Frank talks to a friend of Barry’s, Dorry Milner (Pauline Challoner).  She’s convinced that the blame for Barry’s current situation can be firmly laid at his father’s door.  “He screwed up Barry pretty efficiently.”

There’s no pat resolution to this story.  Marker was paid to do a job, which he did to the best of his ability.  Barry’s decision to plead guilty manages to negate most of Frank’s investigations – so what we take away from Case for the Defence is the unscrupulous nature of Ben Osbourne and his assertion that the truth can be bought.

Marker’s rarely in the position to be able to pick and choose his clients and his conflicts with them, when he comes to realise that their aims are ones he is morally unable to respect, will fuel the drama of many of the episodes to come.