Labour took Sheffield Hallam from the Lib Dems, unseating former deputy Prime Minister Nick Clegg in the shock result of the 2017 election.
But Jeremy Corbyn's party face a three way battle to hold the seat, after it was left effectively vacant by scandal-hit Jared O'Mara.
The Lib Dems hope to capitalise on swing voters losing trust in Labour over O'Mara's selection.
Olivia Blake, the Labour candidate hoping to replace him says O'Mara's name does sometimes come up on the doorstep.
But she didn't get the impression it would have a heavy impact on the vote.
"I think half the time people raise Jared because they like a gossip," she said.
Despite having returned Lib Dem MPs from 1997 to 2015, the seat is a three-way marginal - and was a safe Tory seat for most of the 20th century.
And the Conservatives returned 24% in the last election - mostly drawing voters away from the Lib Dems.
Labour's candidate in the seat, Olivia Blake told the Mirror even more locals said they planned to vote Tory this year.
"It's even worse this time," she said. "We've spoken to 1,000 people who say they're going to vote Tory. And they normally just don't tell you."
And with students making up a huge chunk of the population, the Lib Dems have taken a kicking in recent years over the coalition years - both in Westminster and in local government, where the formerly Lib Dem controlled council is now solidly Labour.
Hallam is the ninth least deprived seat in the UK - a combination of leafy streets of semi-detached houses and rows of terraces rented to students.
The 2001 census shows it has the highest proportion of people classified as professionals of any UK constituency.
And 60% of working age people hold a degree.
Hallam voted to remain in the EU by 66% - bucking the trend in the city which narrowly voted Leave overall.
And every voter the Mirror spoke to raised Brexit as a major concern - even more important than local issues.
Wendy Taylor, 74, said she would be voting Lib Dem, because they would "definitely" keep the UK in the EU if they won.
"That's very important," she said. "And I don't have any confidence in the other two leaders at all."
She also said she wanted to see controls on executive pay, more help for elderly people and more money for the NHS - as well as for the country to turn away from consumerism.
"The reason we're in this mess is greedy consumers," she said. "It's greed that has landed us in this, and that was Margaret Thatcher in the 80s."
Shahla Alghasi, 52, said she was voting for Labour because she liked "the character of Corbyn."
"Because I work for the NHS," she said, "definitely the Conservatives' plan is to make the NHS like the private sector. They'll really destroy the NHS. That's why I'm voting Labour.
"But also, for Brexit. I'm really worried for it. Because we don't have a good deal to come out and I'm sure it would have a negative effect on the economy of the country."
Aside from Brexit, Ms Blake said, the big issues are, "buses. A lot.
"They've really had a lot of cuts to services in this area."
"The NHS is massive," she said. "And education."
But she said the local council's controversial programme of tree-felling, which sparked outrage in the city's leafier areas, was "nothing like" the hot-button local issue it once was.
Last December councillors came to a compromise with campaigners, agreeing that no healthy tree would be felled unless there was no other option.
Ms Blake said: "It comes up every now and again. I think people realise that we have moved things forward."
