Northampton have turned the ball over in the middle of the pitch and Billy Vunipola is having a little tete a tete with the referee after his side are penalised for coming in at the side. It's not been the hosts' day so far.

Nope, the referees aren't having it. They've seen an obstruction by Will Fraser in the build-up, so Duncan Taylor's score in the corner for Sarries is chalked off. 

Penalty to Saints and they kick to touch. 

Paul Grayson
Former England fly-half on BBC Radio 5 live

"Jerome Garces needs to have a look at that just because there was a collision somewhere in midfield."

Have Saracens made the ideal start to the second half? Duncan Taylor is over in the corner, after some good handling from Chris Ashton, but it's gone to the TMO for an infringement in the build up...

A tactical replacement for Saracens, as Neil de Kock replaces Richard Wigglesworth at scrum-half. 

Northampton are without a number of key players today - Dylan Hartley, George North, Lee Dickson - but they're edging this one against Premiership rivals Saracens.

We're 40 minutes away from finding out who's going through to the semi-finals. 

Chris Jones
BBC rugby reporter

"It could still be a great season for Exeter but it's a tough pill to swallow because they were so close to winning. If you said to Rob Baxter, Champions Cup semi-final or Premiership final, he'd take the latter. It's a club on the rise."

Let me just remind you of the madness that occurred in the first quarter-final of the Champions Cup. 

In summary: Wasps went ahead, Exeter recovered and led by 13 points, but it was Wasps who went through with the last kick of the game. 

Knockout rugby at its best. Read all about the drama here.

Image source, Getty Images

Richard Wigglesworth tries to toe-poke Sarries forward from a scrum but the ball is soon kicked into the crowd for half-time.

A Ken Pisi try gives Saints the advantage. Can the Premiership champions recover?

Referee Jerome Garces gets some boos from the partisan home crowd after he pulls Saracens up for a forward pass when they thought they were away while playing advantage. 

Their consolation is a penalty. 

Farrell kicks to touch for a line-out and Saracens' forwards try and push towards the line from inside the Saints 22, but they are turned over Stephen Myler boots clear. 

Image source, Rex Features

Saracens are trying to make the breakthrough in attack but some brilliant work from Saints flanker Ben Nutley sees the ball turned over. 

Saracens are forced back into their own 22. Owen Farrell's booming kick goes straight to Saints full-back Ben Foden. It's back and forth at the moment. 

Jamie Elliott rips it up the far flank for Northampton and almost reaches the 22 metre line. My, he's a speedy one. 

Sarries are pinged and Stephen Myler decides he wants to go for the points. It's not the easiest of kicks, but he manages to get it right. 

George Pisi feeds out to brother Ken on the right and it's another penalty as Duncan Taylor tries to pull down one of the speedy brothers. 

Stephen Myler doesn't seem to be trusting his kicking. Saints have gone for the corner again.

Heave-ho! Heave-ho! It's off the Saints go. They drive a maul forward and gain some decent metres.

But Alex Goode collects a cross-field kick aimed for Ken Pisi and Saracens have it back.  

Northampton earn a penalty after a maul is pulled down and they kick for the corner, as they try to capitalise on their decent driving game.

But the line-out fails when Courtney Lawes drops the ball, and it's a Saracens scrum in their own 22.

Image source, PA

First scrum for Saints deep in their own half. It's booted forward but Sarries gather possession and they get back over the half-way line.

They're awarded a penalty as Saints fail to roll away and Owen Farrell has a go from the centre circle. It's good, they get the points.

And Will Fraser is back on after a spell on the naughty step.

Jamie Elliott goes steaming forward on the left flank, charges straight through Richard Wigglesworth, and touches down in the corner.

It's gone to the TMO and unfortunately for Saints, it shows the winger knocked on as he tried to dot the ball down.