The appearance of a rebel amendment on the Queen's Speech, regretting the lack of a referendum on Britain's EU membership, has transformed the debate from ritual combat to something much more threatening for the government.
Most of the names attached to it so far are pretty predictable - although former leadership contender David Davis picks his battles pretty carefully, so his appearance in the list is significant.
But it will be worth watching to see if UKIP's strong showing in the county elections results in some MPs supporting the amendment to protect their position in their constituency....
Will there be a correlation between UKIP council gains and sudden outbreaks of backbench euroscepticism from previously quiescent Tories?
Of course, the amendment will almost certainly be defeated, pretty comfortably, and would not bind the government to hold a referendum, even if won. But a major rebellion - and the prospect of future amendments to actual legislation, or a private members' bill to hold a referendum (see Thursday's entry, below) - would signal a very difficult year for the government in the Commons. To put it mildly.
There are several different currents of opinion on the Conservative benches on the exact form any referendum, but I think the broad demand that the Conservatives should push for some kind of vote before the next election (if only to flush out Labour and the Lib Dems into opposing it) unites them all.
Here's next week's rundown:
The Commons convenes at 2.30pm for another day's debate on the Queen's Speech - where the theme will be Health and Social Care, one of the major bills in the government's programme.
The rather unpromising looking adjournment debate on "Cleveland Fire Authority mutualisation" led by Middlesbrough Labour MP, Tom Blenkinsop, could actually prove to be rather interesting and important. The government is keen to encourage workers in public services to form mutual companies to deliver them, as a way of encouraging greater efficiency, flexibility and employee engagement in delivering better services. The Chief Fire Officer and government have been looking at a "mutualisation" model for the Cleveland Fire Service.
And Mr Blenkinsop warns that the original assurance by ministers that this isn't privatisation by the backdoor has been undermined by revelations that any mutualised fire authority would have to allow private sector tendering because of European procurement legislation. He fears mutualisation will expose English fire services to private sector take over.
In the Lords (from 2.30pm) they are holding a daily question time - and the subjects to be raised include some topical issues: steps to improve the implementation of the NHS 111 service, UK clothing sector retailers ensuring that people working throughout their supply chains enjoy safe and secure working conditions and the proposals by the newspaper industry for an alternative regulation system - that one comes from Leveson Report supporter and former Conservative party chairman Lord Fowler.
Then peers move on to their debate on the Queen's Speech - where their subject of the day is business, economy, local government and transport.
The Commons meets at 11.30am when question time will be back - in the form of Treasury Questions. The theme for the day's Queen's Speech debate is the cost of living. And the day ends with an adjournment debate led by the Conservative Charlotte Leslie on "Enforced monopolies in council sport provision". She's unhappy about Bristol City Council's policy towards swimming clubs - an issue which she warns could undermine the Olympic legacy.
In the Lords (from 2.30pm) questions to ministers range across local authorities requiring bailiffs to pay them part of the fees charged to debtors, and a levy on single use plastic bags in England. Then the debate on the Queen's Speech focuses on agriculture, culture, education, energy, health and welfare.
The Commons meets at 11.30am for Welsh questions, and then, at 12pm, prime minister's question time. (It's worth noting this is the first PMQs since 24 April - and David Cameron won't face another one until 5 June, because MPs will depart for their Whitsun recess on Tuesday 21 May. They than face a marathon seven weeks without a break - departing for the summer on 18 July.)
After PMQs, the debate on the Queen's Speech focuses on economic growth - this is the point at which amendments, from Labour and, possibly from rebel Tory backbenchers, will be voted on. Could this be the first rebellion of the new Parliamentary year....just one week in? Incidentally, Labour's line is that they think the focus should be on jobs and economic growth - and that the UK should be pressing for reform in the EU, not threatening to leave. They're coy about their whipping policy on the day - but that rather suggests they'll vote against.
The day ends with an adjournment debate on dangerous dogs and Jade Lomas Anderson. Following the death of Jade, a 14-year-old constituent in Bolton West, Labour's Julie Hilling is campaigning for proposed changes to the law on dangerous dogs to go further than simply making it possible to prosecute owners for attacks on private property. She argues measures, including compulsory micro-chipping of all dogs and Dog Control Notices, are needed to tackle the irresponsible owners before an incident takes place.
In the Lords (from 3pm) questions to ministers cover the new under-occupancy rule for housing benefit and budgetary support to developing countries in 2013-14. The theme for peers' final day of debate on the Queen's Speech is defence, foreign affairs and international development.
Before MPs gather in the chamber there'll be more attention than usual focused on the annual ballot for debating time for private members' bills - because there's a chance that one of the winners will seize the chance to put down a bill for an EU referendum. It all depends which name is drawn out of the hat - in a slightly sexed-up ceremony which will involve the names been drawn out in reverse order, so the MPs with the lowest priority will be announced first, allowing suspense to build towards the announcement of the honourable member who'll be in poll position. The ballot starts at 9am.
When the Commons meets at 9.30am the first business is Environment, Food and Rural Affairs Questions, followed by a series of shorter questions directed at the MPs who speak for an assortment of outside bodies; the Church Commissioners, the Public Accounts Commission and Speaker's Committee on the Electoral Commission. That is followed by the weekly announcement of forthcoming Commons business, by the Leader of the House, Andrew Lansley.
The main debate of the day, chosen by the Backbench Business Committee, is a debate on mental health - an issue raised by backbenchers like the Conservative Charles Walker and Labour's Madeleine Moon.
The adjournment debate, led by the Conservative Mark Spencer, is about sentencing for people convicted for road traffic offences.
Over in Westminster Hall (from 1.30pm), MPs have a chance to debate on the two select committee reports; the Education Committee's report on careers guidance for young people and the Science and Technology Committee's on educating tomorrow's engineers.
In the Lords (from 11am) ministers field questions on funding to allow severely bullied children to return to education, and government proposals for reform of the EU at the forthcoming meeting of the European Council.
That is followed by debates led by backbench peers. Lib Dem Lord Greaves raises the contribution of outdoor activities to the UK economy and to the health and wellbeing of the population, and Labour's Lord Soley discusses the current level of growth in the UK economy.