The Durban side beat the Cheetahs 34-20 in Bloemfontein last week to make it three wins in a row and consolidate their sixth place in the overall standings.
Their impressive run comes after an inconsistent start to the season in which they lost five of their opening nine games.
They face arguably their biggest challenge this season when they host table toppers the Stormers in Durban on Saturday.
While many have praised their change of fortunes, Plumtree said each game posed a different threat.
“We have to make sure we remain focused on each week," Plumtree said on Wednesday.
“Our preparation has been good so far this week and we’re just looking forward to this one on the weekend.”
Looking back at the win in the Free State, which was their third in succession over the Cheetahs, Plumtree conceded it was one of the best this season.
“That was definitely a pass mark,” he said.
“Every time we go up to Bloemfontein and win is really good for us. It’s a tough fixture.
“I thought the boys played some lovely rugby. To get five points up there is outstanding.
“Defensively, we let ourselves down a bit at times, but there was some really good attacking play.”
Though the win was pleasing, Plumtree added that an injury to centre Tim Whitehead, who has become an integral part in their midfield this season, was a major set-back for the Durban-based outfit.
Plumtree confirmed that Whitehead did not train earlier in the week.
The former Stormers midfielder has a groin problem and is a doubtful starter against his former franchise, but flyhalf Patrick Lambie, a late withdrawal against the Cheetahs due to flu, is expected to return.
Plumtree believed his side would have to be at their best to get the desired result against the Stormers.
“They’re top of the log, an outstanding side and very clinical in what they do,” he said.
“They have enjoyed a lot of continuity in selection and they’re a very efficient outfit, so we know that we’re going to have to play very well to beat them on the weekend.”