Is there an expression or idiom for something convenient that happens right when you need it to?
Especially if it's something unlikely. Almost as if it could only happen in a movie. For instance, you're about to be robbed and a random cop on patrol arrives at that exact time. What are the chances of that?
Is there an expression/idiom that communicates that general idea?
Solution 1:
The first word that comes to mind is serendipity. Merriam-Webster says:
luck that takes the form of finding valuable or pleasant things that are not looked for
But as Robusto correctly points out, that word is mostly used for discoveries. A thesaurus points from there to fluke, defined by macmillan as:
something that happens unexpectedly because of an accident or good luck
An alternative option, as Brian Donovan points out, is the adjective fortuitous, as Merriam-Webster describes:
2 a : fortunate, lucky
b : coming or happening by a lucky chance
Solution 2:
Godsend (noun):
an unexpected thing or event that is particularly welcome and timely, as if sent by God Dictionary.com
something good that happens unexpectedly, especially at a time when it is needed CDO
'The grant was a real godsend, especially considering the theatre was due to close next month.'
Solution 3:
To further the idea of 'Something that could only happen in a movie, perhaps Deus Ex Machina:
Deus ex machina (Latin: [ˈdeʊs ɛks ˈmaː.kʰɪ.naː]: /ˈdeɪ.əs ɛks ˈmɑːkiːnə/ or /ˈdiːəs ɛks ˈmækɨnə/;1 plural: dei ex machina) ... The term has evolved to mean a plot device whereby a seemingly unsolvable problem is suddenly and abruptly resolved by the contrived and unexpected intervention of some new event, character, ability or object.
Wikipedia
Solution 4:
Stroke of Luck
A fortunate occurrence that could not have been predicted or expected
Jim: How'd you get a ticket to the game its been sold out for weeks?
Tom: A bicyclists happened to run into me this morning and took off. Afterwards I noticed the ticket on the ground, it must have fallen out of his pocket. What a stroke of luck right?
Solution 5:
For yet another expression with heavenly implications and origins, there’s
meaning: “something that you need which you get when you are not expecting to get it.” (from Cambridge Idioms Dictionary, 2nd ed., as cited in The Free Dictionary)