The third episode of Vigil has been eagerly awaited by fans after the debut double bill left people on the edge of their seats. 

The third instalment in the six part series is due to air on Sunday September 6, offering fans further insight into the goings-on at Dunloch naval base. 

Following an early plot twist in the first episode, viewers have been unsure as to which members of the cast will feature in each episode. 

There is a particular question mark over Martin Compston's character, with the promise of an appearance from the Scottish actor initially encouraging many people to tune in to the drama-thriller. 

Here's what we know about the plot for episode 3 and whether Martin Compston will feature...

What is the plot for episode 3 of Vigil?

According to the BBC's plot summary of episode 3, the investigation will take Kirsten "to the heart of Scottish politics". 

It reads: "Kirsten believes the murders were part of a coordinated attack. Her investigation takes her into the heart of Scottish politics and the naval cover-up of a near catastrophe in the US.

"Amy starts to question who she can trust on Vigil, when a message from Kirsten makes her realise she is being deliberately undermined."

Will Martin Compston feature in episode 3 of Vigil? 

After an early plot twist, fans have been left wondering just how much Martin Comspton will appear in the show. 

While we can't be certain of the answer, his name does appear in the credits for episode 3 which suggests he will make some sort of appearance, however big or small. 

What is the cast line-up for Vigil?

Martin Compston is not the only famous face in Vigil. 

Suranne Jones, famed for her lead role in Doctor Foster plays Amy Silva. 

Aberdeen born Game of Thrones star Rose Leslie plays Kirsten Longacre, while Paterson Joseph of Noughts + Crosses plays Newsome. 

Leslie's Game of Thrones colleague Stephen Dillane plays Shaw, with Adam James playing Prentice and Sex Education's Connor Swindells playing Hadlow. 

Rounding off the cast is Shaun Evans as Glover.