First it's the euro-referendum, then assisted dying: Parliament's back for a brief pre conference-season thrash - with some very big-ticket legislating at both ends of the week.
So what's on?
The Commons returns at 2.30pm and opens with work and pensions questions. This being the first day back after the long summer break, the chances are there will then be some urgent questions or ministerial statements before we get on to the day's scheduled legislating. There is no shortage of possible subjects, with everything from the refugee crisis (Andy Burnham has a UQ request down) to government policy on renegotiating the UK's membership of the EU, to Trident replacement.
One side effect of airing these important issues is that the crucial report stage proceedings on the European Union Referendum Bill could be delayed for a couple of hours, and then stretch on into the night, with key votes not taking place until midnight.
Anti-EU Tories have been organising furiously to ensure that their forces are marshalled. And in an amendment paper of fiendish complexity, there are a galaxy of proposed changes to the legislation.
The main area of contention is on the restrictions placed on campaigning by the government and the EU during the referendum. The Foreign Secretary, Philip Hammond, has put down detailed amendments on this issue, after running into criticism during the committee stage debates on the bill, but they only appeared at the last minute, and as I write, the very detailed small print was still being studied by suspicious eurosceptics.
In a round-robin to Conservative MPs, the Europe Minister David Lidington says the government has reinstated Section 125, (the Purdah regulations from the Political parties Elections and Referendums Act 2000) with a tweak to allow "business as usual communications on EU-related matters", but it would prevent the government using billboards, newspaper or digital advertising or mailshots or emails to influence voters in the 28 days before the poll.
The exceptions he proposes are to allow ministers to promote UK interests by issuing statements on EU Council meetings or in response to ECJ judgments. There might be a European or international emergency, like the Mediterranean migrant crisis and he says the government should not be prevented from speaking in the campaign period.
But the key issue is a new clause allowing the government powers to issue specified communications during the referendum period, by statutory instrument, after consultation with the Electoral Commission. Conservative eurosceptics say this amounts to the same position which led them to clash with the government at the bill's committee stage - an invitation to trust ministers to do the right thing. Because the new amendments were not published until very late, they have yet to agree tactics, but key figures like backbench organiser Steve Baker are clearly not happy, arguing that a requirement to consult the Electoral Commission was not a sufficient safeguard for an enabling power.
On other issues, there are amendments and new clauses to ensure EU institutions neither campaign nor bank-role campaigning. The Labour front bench has, helpfully, proposed a series of amendments which could attract the votes of Conservative rebels.
Other highlights include a call from the SNP (New Clause 3) for a "double majority" rule, under which the UK could only leave the EU if there was a majority for doing so in each of the four constituent nations - so even if there was a numerical majority for withdrawal across the whole of the UK, Britain would remain in, if there was a majority voting to stay in one of Scotland, Wales or Northern Ireland.
Sir Bill Cash and others (New Clause 1) call for a Broadcasting Adjudicator to oversee the impartiality of coverage of the referendum; they would draw up guidelines and deliver rulings on any complaints within one day.
Hardcore EU opponents Philip Davies and David Nuttall (NC4) want to require that in the event of the UK voting to leave, notice would have to be served on the European Council under article 50 of the Lisbon Treaty, within 28 days of the referendum. Withdrawal would have to be completed within two years, and their clause would forbid any further referendum. (Ministers have backed another amendment from these two, ruling out the referendum taking place alongside local elections on 4 May 2017 and Mr Hammond has added his name to it.)
Labour Europhile Mike Gapes wants to allow EU citizens resident in the UK to have a vote (Amdt 20).
Of course, it's not a done deal that all of the above backbench amendments will be selected for debate - the chair will announce the choice at the start of proceedings.
Over in Westminster Hall, my eye was caught by a couple of debates, including business rates in rural areas - the Conservative Jake Berry's (from 11am - 11.30am) on what he calls "mission creep" by the National Valuation Office. He says new policies on the treatment of hole in the wall cash machines and on domestic stables could have damaging effects on the rural economy.
Adam Holloway, another Conservative, has a debate scheduled on Mediterranean migration (2.30pm - 4pm) but it's possible this will be overtaken by events in the main chamber.
In the Lords (2.30pm) the main legislating is the first committee stage day on the Energy Bill - the key issues both today and on Wednesday will revolve around whether the proposed Oil and Gas Authority will be fit for purpose.
Peers will debate amendments on the precise functions of the OGA, whether there should be a requirement for it to have regard to environmental considerations, climate change, carbon capture, transportation/storage, and decarbonisation of the industrial sector.
And that's followed by a Labour regret motion against the Criminal Legal Aid (Remuneration etc.) (Amendment) Regulations 2015 - which cuts payments to lawyers for legal aid work, from Labour front-bencher Lord Beecham. This is the kind of move likely to attract the support of the legion of ex-judges and superlawyers on the cross-benches, so ministers should watch out.
The Commons day opens (at 11.30am) with justice questions, followed by a ten minute rule bill proposed by the Conservative Ian Liddell-Grainger on the Satellite Navigation (Updating Scheme).
After that, there may well be more post-holiday ministerial statements or urgent questions. And then it's on to the detail of the Finance Bill in its committee stage. Labour's shadow Chancellor Chris Leslie has amendments down calling for a report on the impact of key measures - the big increase in Insurance Premium Tax on the cost and take-up of insurance policies (in the Budget debate he condemned the increase as "a tax hit on the insurance of the family home") and report into the effect of the removal of the Climate Change Levy exemption on the renewable energy generators.
In the Lords (from 2.30pm), the main debates are on two select committee reports. First, the Communications Committee report on women in news and current affairs broadcasting, and then the report from the EU Committee on civilian use of drones in the EU.
There will also be a short debate on plans to boost productivity in the United Kingdom
The Commons meets at 11.30am for Welsh questions, followed at noon by prime minister's questions - this will be Harriet Harman's last outing as acting leader of the Labour party. She has faced David Cameron 15 times as acting leader of the Labour party, and when PMQs has been delegated to deputies she has faced William Hague 12 times, and Nick Clegg seven times.
Labour MP Kerry McCarthy - one of Parliament's small contingent of vegans - has a ten minute rule bill on cutting food waste - and the main debate will be on a subject to be chosen by the SNP.
In Westminster Hall, there's a promising-looking debate (9.30am - 11am) on affordable housing in London - new Conservative MP Chris Philp is concerned that housebuilding in London is failing to keep pace with demand, and he's keen to highlight the case for releasing publicly owned land (the 6,000 acres owned by Transport for London, for example) for housing development.
Other subjects to be aired in Westminster Hall include contaminated blood products (11am - 11.30am); funding for West Midlands Police (2.30pm - 4pm); orphaned opencast mines (4pm - 4.30pm) and dementia care services.
In the Lords (from 3pm), peers are focusing on the detail of the Energy Bill and there will be a short debate on the national strategy for the treatment of lymphoedema in the NHS.
The Commons meets at 9.30am for Environment, Food and Rural Affairs questions; plus mini-question times for the MPs who speak on behalf of the Church Commissioners, the Public Accounts Commission and the Speaker's Committee on the Electoral Commission.
The weekly Business Statement from the leader of the House will follow; will it reveal a new parliamentary strategy to corner the new leadership of the Labour party on contentious issues like Trident replacement and benefits cuts?
Then MPs turn to the first Backbench Business Committee debates of the 2015 Parliament: first on immigration detention (the subject of a scathing report by a high-powered All-Party Group, shortly before the general election) and then on Sustainable Development Goals.
In the Lords (11am), there are debates on subjects chosen by backbench Labour peers, starting with Lord Haskel, on the British economy beyond austerity - followed by the future financing and independence of the BBC, led by Baroness (Joan) Bakewell.
And during the dinner break there will be a short debate on the effectiveness of the UN and the selection process for Secretary-General and other appointments, led by Lord Dubs.
The Commons private members' bill season starts with a bang (9.30am) with the second reading of Rob Marris's Assisted Dying (No. 2) Bill.
This will be a classic private members' bill tactical battle, with opponents seeking to talk the bill out, and supporters hoping to muster enough MPs to force a vote and get the bill through to detailed scrutiny in committee. No-one seems to have much idea how it will play out, because this is the first real test of the 2015 Commons on this kind of free vote issue.
One factor may be that the SNP are unlikely to vote on what will be an England-only measure, whereas the solid group of Catholic Scottish Labour MPs they replaced would have been a key part of any coalition against a bill of this kind.
It's possible Labour MP Vicky Foxcroft might get a chance to introduce her Representation of the People (Young Persons' Enfranchisement and Education) Bill. (This cause is popping up all over the place at the moment - and will also certainly feature in debates on the EU Referendum Bill. Supporters of lowering the voting age seem determined to add amendments to every possible piece of legislation.)
But I'd be surprised if we make it to Mark Pawsey's Crown Tenancies Bill, let alone some of the many measures lurking further down the order paper. But keep an eye on two, in particular; David Davis's Public Nuisance from Wind Farms (Mandatory Liability Cover) Bill is a carefully calculated swipe at onshore wind farms and he's far too wily a tactician to let it languish, undebated.
Another old hand is Graham Allen, whose Constitutional Convention (No. 2) Bill parallels the measure proposed in the Lords by the Lib Dem Lord Purvis of Tweed.
And there are also private members' bills in the Lords (from 10am). First is the Council Tax Valuation Bands Bill proposed by Lord Marlesford, which would create a new set of council tax valuation bands to apply to all dwellings bought or sold after 1 April 2000.
Next is the Earl of Lytton's Property Boundaries (Resolution of Disputes) Bill at second reading - this deals with disputes over boundaries and private rights of way or the title of an estate.
And the Conservative Lord Trefgarne is having another stab at his Succession to Peerages Bill, which seeks to give women an equal right to inherit hereditary titles.