Upon returning to her family home for her Grandfather?s christening, a head-strong young woman and her suspicious foreign fianc? must prove their relationship to the assembled guests ? including an undercover agent from the Immigration Office!

A logline should explain Act I, Act II without revealing Act III.
When I said that it was an old concept, it is not a criticism. It means that you need to have a hook, a gimmick that makes your script stands out.

When a bookish young woman is forced to attend her grand father's baptism, she must convince both her family and an undercover immigration agent that her new fianc? who she met online has no ulterior motive.

Luke:
To clarify, where I come from, christenings refer to infant baptism; otherwise, we just called it baptism. (And I have witnessed adult baptisms, too.) Again, I'm only saying some people might be confused by the terminology. But if the ritual (independent of what it is called) works for the story, dovetails with the theme (does it?), then go for it.

>>> you?re spilling your plot unnecessarily.

A logline should tell the reader where the story is going (whether or not it gets there). It should never give away the ending or a big reveal, but...

>>> I know it?s an old concept

There's your predicament. If it's already been done so often, the first question in most people's minds in Hollyweird will be: why do it again?

>>spin it in a different direction.

Well, what new take do you have on the premise that spins it in a different direction? (Again, without giving away the ending.) The baptism isn't a "different direction" because it's not what the story is about; it's only an incident that brings the family together. And then what happens?

Valetin - I'm glad to hear someone else has had a similar experience to me, re: an elderly person getting christened. I didn't think it a particularly outlandish and unrealistic idea.

I appreciate the comments, but again - I feel these concerns that should (and would) be confronted and resolved within the script. That a) you'd be cluttering up the logline by trying to include more, and b) you're spilling your plot unnecessarily. That said, perhaps I'm misunderstanding what the actual purpose of a logline is. I guess the idea is to try and find a way to allude to the complications, without explicitly stating them.

And yeah, I know it's an old concept, there are plenty of other things with the same premise, Green Card, the sitcom Spaced. I remember when Roger Ebert reviewed The Proposal, he said that the situation was old when Tracy & Hepburn did it. So I'm not particularly bothered by that - my feeling about this sort of thing is that you take a situation the audience thinks they're familiar with, and then spin it in a different direction.