|Venue: Principality Stadium, Cardiff Saturday 12 February Kick-off: 14:15 GMT|
|Coverage: Live streaming on BBC One and BBC iPlayer. Live commentary on BBC Radio 5 Live.|
After the 2019 Rugby World Cup, Scotland's limping exit from the pool-stage and the embarrassment it brought, it was time to remake the blueprint.
Gregor Townsend was at that time under great pressure and hired an Australian Welshman to be his new defence lieutenant.
They have been instrumental in shaping a new, more meaner Scotland, one that loves defending and is fiendishly difficult to beat.
They will be heading to Wales this weekend, Tandy's home country, to find more history after winning back-to-back Calcutta Cups.
Tandy didn't change Scotland's fortunes by himself, but he was a major player in the process. Tandy had the tools to implement a major pragmatism transplant in 2019, in order to match their high-octane strategy of playing the fastest rugby in the globe.
He switched the way Scotland defends. They encouraged players to take more control of their shots and contest the breakdowns. They were open to Tandy’s new system and its workings.
Tandy's 2020 campaign was his first in the role. In that year, Scotland conceded five attempts, the lowest total in the championship, and a Scottish record. The tournament's joint-best return was 10 years later.
This is a stark contrast to the other Six Nations that Townsend had previously established.
Scotland's defense was leaked more than the Titanic in 2019. They were subject to 17 tries. They lost 14 games in 2018. They were only beaten by Italy more often.
They have played England three times now with Tandy as their defence supremo, and conceded just three tries.
The picture will be even more convincing if you examine the numbers in detail.
Scotland missed 11 tackles per match last year. With 91%, they had the highest tackle success rate. They were the least likely to give up a line.
England asked Scotland for 140 tackles. Scotland missed just eight of these, which is almost 94%.
Tandy was fired as Ospreys' head coach four years ago. BBC Scrum V Twitter account was criticized for captioning a photo featuring the dejected-looking coach and ‘Ta Ta Tandy.
He was a stalwart in his region and was a Pro12 champion in the first season of his helm in 2012. The fall of the axe was devastating.
Tandy was only 32 years old when he became a club boss. Tandy went to Australia to work for the Waratahs. He was exposed to new styles and structures, and gained valuable wisdom. On his watch, the Waratahs' points-conceded-per-game figure shrivelled by nearly 10.
Warren Gatland was inspired by his work with Scotland to appoint him as defence coach for the British and Irish Lions tour through South Africa. He will be able to gain valuable insight into Six Nations rivals.
Kurtley Beale of the Wallabies, the great full-back, as well as Ronan O'Gara of Ireland, the wily former pivot and La Rochelle Coach, are two luminaries who have sung his praises. Stuart Hogg described him as the “best defence coach” in world rugby last week.
Since 2002, Scotland has not won Cardiff and only once in Wales since Tandy's debut in Llanelli. They will continue to draw on his influence to break new ground.