Venue: Twickenham, London Date: Saturday, 10 February Kick-off: 16:45 GMT
Coverage: Watch live on S4C; listen on BBC Radio 5 Sports Extra, BBC Radio Wales & Radio Cymru; text commentary on BBC Sport website and app.
Wales only have a matter of days to get their game right to face England at Twickenham on Saturday.
There are some harsh lessons to learn from the narrow 27-26 loss to Scotland in Cardiff.
Aaron Wainwright believes young Wales can take confidence from that stunning second-half comeback, though admits they cannot afford a similar start.
Warren Gatland admitted the first half was the worst of his rugby career, so what changes will the head coach make?
Scarlets fly-half Ioan Lloyd put forward a strong case for the number ten jersey, though is tipped as a future outside centre by Jonathan Davies while fellow pundit Tom Shanklin would see him on the wing.
"He has played there in the past for Bristol but I just think you want him on the field somewhere," Shanklin told Scrum V.
"He makes a difference and can do things that no-one else in the team does."
Gatland is due to name his team to face England on Thursday.
All eyes are on Gatland's selection at numbers nine and ten following the extreme contrast in the two halves against Scotland.
His hand could be forced if Costelow fails to recover from a second head injury in recent weeks, opening the door for Lloyd to make a first start in four years - and the first with a crowd.
Lloyd helped turn the game on its head with his range of passing after Costelow had been utterly out-played by the wily Finn Russell.
Gatland admitted it was a close call not to start Tomos Williams, the in-form scrum-half in Welsh rugby this season.
Gareth Davies got the nod to help his Scarlets teammate Costelow through his Six Nations debut.
But between them they missed five tackles, executed a flawed kicking strategy and failed to create a point.
Ex-Scotland captain John Barclay said: "I feel sorry for Davies and Costelow because they looked like they were simply doing what they were told from the first minute.
"The kicking game is important but when you're at home, at the start of the tournament and the first thing you do is kick the ball away, you could feel the crowd come down. It feels like you're just playing not to lose."
Wales had 100% success rate at the scrum but once again the lineout - their Achilles heel in the World Cup quarter-final loss to Argentina - faltered.
Wales lost six of their own throws and while there are many moving parts to a lineout, the hooker is always exposed.
That could prompt a switch from Ryan Elias to Elliot Dee, an unsung star with two World Cups, two Six Nations titles and almost 50 caps to his name, who was a dynamo around the pitch.
Will Rowlands has returned to training after missing last week following the birth of his child and would be tipped to start having been among the first names on Gatland's team sheet at the World Cup.
Leon Brown tackled hard on his Test return but replacement Keiron Assiratti also proved far livelier around the field.
Prop Dillion Lewis and lock Seb Davies have both been added to the squad.
George North is available having rested a shoulder injury last week and will surely make an immediate return.
Four times Wales got into Scotland's red zone in the first half but came away empty-handed each time.
Nick Tompkins failed to create openings and conceded three turnovers, more than any other player.
Owen Watkin made little impact and was replaced by Mason Grady, who could be deployed either as a 13 or wing if Josh Adams pays the price for his petulance.
Adams cost his side three points after throwing away the ball and Gatland was scathing of the experienced wing given the one-point losing margin.
"The Josh Adams [penalty] was dumb," said the head coach.
"When you think about it, that's the difference between winning and losing the game."
Aaron Wainwright was man of the match, despite the loss, while Tommy Reffell's turnovers kept Wales just about in the game.
However Gatland is still looking for balance in his back-row with the likes of Taulupe Faletau, Jac Morgan, Taine Plumtree and Josh Macleod all injured and try-scorer James Botham released back to Cardiff after suffering knee damage on Saturday.
New-cap Alex Mann took over at blind-side and like Botham was a try scorer against Scotland.
Gatland may feel he needs more size for Twickenham in which case either of the Cardiff forwards Teddy Williams - another to make an impact on Saturday - or uncapped Mackenzie Martin could be an option, with lock Davies an additional back-row option.