One, stiff and engraved, is effectively to say goodbye to a former leader. The other is a summons to the home of the party's newest, brightest star.
That the Queen and Tony Blair have been persuaded to attend Baroness Thatcher's 80th birthday party testifies that it is likely to be her last major public outing. They are among 650 guests gathering in the Mandarin Oriental Hotel's gold-embossed ballroom on Thursday.
Others include most of her former Cabinet colleagues and showbusiness stalwarts such as June Whitfield and Sir Tim Rice.
The party is being organised by Lady Elizabeth Anson, who hosted her 70th birthday party at Claridge's. Then the guests, who included Sir Michael Caine and Frederick Forsyth, sat down to a full meal. Thursday's event is limited to two hours of drinks.
And although the Hyde Park hotel will ring to the sound of the Tories' 1980s hey-days on Thursday, it is the other, less grand, invitation that is the hotter ticket.
It is to join "Dave" and "Sam" Cameron at their Ladbroke Grove home for a plate of lasagne and a few bottles of good - but not outstanding - wine. The young contender is inviting select groups of undecided MPs to his west London home for a series of dinner parties. Just as Tony Blair used his Georgian townhouse in Islington to seduce allies, so, a decade later, his would-be successor is clinching support for his leadership bid over supper.
"I would say it is more homely than chi-chi but all the more charming for that," reports one MP who admits he was won over in the course of a dinner party chez Cameron.
As "Sam", 34, helped prepare a simple lasagne in the kitchen, "Dave" poured wine into modern glassware and set to work persuading the new MPs he should be the next Tory leader.
Although the 39-year-old received a huge boost at last week's Conservative Party conference in Blackpool, he still must persuade his parliamentary colleagues he should make the final run-off.
He will receive the backing of Steven Norris today - a further sign that he is being embraced by modernisers - and is expected to land a "big-name" endorsement in the coming days.
Meanwhile, David Davis is coming under mounting pressure to revitalise his flagging campaign. "We weren't even at the races," said a Davis backer yesterday. "Cameron's campaign was much hungrier, more media-savvy - just better in every department."
In a sign that the former frontrunner is beginning to panic, he has sidelined campaign manager Andrew Mitchell MP. David Willetts and Damian Green have been brought in to help stem the flow. In a bid to prevent defections, publicly declared Davis-backers are being invited to an event in Westminster on Tuesday. "We don't know if it will be a party or a wake," said one grimly.
The one hope for Mr Cameron's leadership rivals was provided last week by his refusal to answer questions on whether he had taken drugs at university. "I had a normal university experience, if you could put it like that," he told a fringe meeting.
His careful choice of words ensured that his time at Oxford is likely to receive close media attention as MPs prepare for the contest, which begins a week on Tuesday. It was with former Oxford friends and family that Cameron celebrated his 39th birthday last night at his constituency home with a dinner of roast pork.