The Ashes could be decided in Canberra. If Australia win and take the four points available it will be securely in their hands - where it has been since 2015.
The series has yet to really lift off after rain washed out the second two T20Is in Adelaide. There is a chance that this match could also be interrupted by showers which may make it a challenge to force a result, although there is the hope that the pitch will have some life.
England captain Heather Knight has been left cursing the weather which has left her side chasing the series, two years after seeing their 2020 T20 World Cup hopes washed away in Sydney only for the skies to clear for just long enough to allow Australia's match to go ahead.
Both sides are talking a positive game in the build-up, but with no red-ball cricket except when Tests are played it is tough for players to get into rhythm. And this time there's only been two days to get ready. At least for Australia it's their second match of the season after facing India, although that was a pink-ball day-night contest.
With a condensed schedule caused by Covid-19 adjustments and the proximity of the ODI World Cup there have been multiple considerations around this Ashes. With an eye on the Test, England kept Lauren Winfield-Hill and Kate Cross out of the T20I set up and let them focus on red-ball preparation.
Cross is one of the players who appeared in the 2013-14 Perth Test which is generally regarded as one of the finest contests in the format where England prevailed by 61 runs despite the all-round brilliance of Ellyse Perry.
Australia have had to contend with a variety of injuries this season and in this series they are now without Georgia Wareham, Sophie Molineux and Tayla Vlaeminck, who would all have pushed for Test selection. However, Beth Mooney is on track for a remarkable return from jaw surgery.
Even in the absence of Vlaeminck, Australia hold the edge in pace with Darcie Brown and Stella Campbell in the squad although England match up well in the spin department. The home side's batting order could be formidable with the likes of Ashleigh Gardner or Tahlia McGrath at No. 7, but England have experienced figures in Knight, Nat Sciver and Tammy Beaumont.
In the spotlight
Ellyse Perry was a central narrative around the T20Is, but because she didn't play, having been dropped as Australia focused on role-specific selection. Her Test credentials, though, do not need a second look: her last three Ashes innings read 213*, 116 and 76*. There will be interest, however, in her role and effectiveness with the ball.
This series could be an Ashes farewell for Katherine Brunt, who has been a huge figure in this generation of the England team. Her first Ashes Tests were back in 2005 when England famously regained the prize and in 2009 she took career-best figures of 6 for 69 at Worcester. She will be key in the pursuit of 20 wickets and also appears set to take on more responsibility with the bat.
Meg Lanning said Australia had a 12 but did not provide further details. Now that Mooney is able to return, Australia's main selection decision would appear to be between an extra frontline spinner or quick bowler. With McGrath and Perry there are plenty of seam-bowling options, but a combination of Brown and Campbell could be tempting.
Australia (possible) 1 Alyssa Healy (wk), 2 Rachael Haynes, 3 Meg Lanning (capt), 4 Ellyse Perry, 5 Beth Mooney, 6 Ash Gardner, 7 Tahlia McGrath, 8 Jess Jonassen, 9 Darcie Brown, 10 Megan Schutt, 11 Stella Campbell
Knight confirmed she knew England's XI but wanted to keep Australia guessing. She did, however, say they were going with an extra bowler compared to the India Test last year which may open the door for a debutant spinner to support Sophie Ecclestone who bowled 64 overs against India.
England (possible) 1 Tammy Beaumont, 2 Lauren Winfield-Hill, 3 Heather Knight (capt), 4 Nat Sciver, 5 Amy Jones (wk), 6 Sophia Dunkley, 7 Katherine Brunt, 8 Sophie Ecclestone, 9 Charlie Dean, 10 Kate Cross, 11 Anya Shrubsole
Pitch and conditions
Having been very green a couple of days ago the surface has since been trimmed. Lanning said she expected some help early on while Knight believes it will flatten out during the game. The forecast has improved somewhat with the opening day looking good with Saturday the main concern.
"We're coming here to win. There's no doubt about that. That's all we've spoken about over the past few days is coming here and how can we best set up a victory. England are coming to do the same thing. So it's certainly not going to be easy, and we're going to have to sort of grind it out through certain periods of the game, but that's the way we're approaching it."
"There's a line of thought that if you bowl first you can dictate the game a little bit more, you still have to take 20 wickets but hopefully you have a chase at the end."