Per @Pheonix2105's answer, in some contexts there might be an implied to [do something to/with] after the word "left". But I don't see that as particularly relevant to the general case. For example...
1: Tom has 10 apples. He gives 3 to Dick. How many are left?
We neither know nor care whether Tom's 7 apples are "to eat", "to give to Harry", or whatever. All that matters is they're remaining (not given away, eaten, or otherwise removed from the original 10 apples).
In such contexts, left is simply an "adjectival" use of the past participle of the verb to leave...
2: Tom has 10 apples. Dick takes 3. How many does he leave?
Note that the last sentence there could just as well have been "How many does this leave?" - it's not really important whether we think of Dick as the "subject" who "leaves" (doesn't take) the leftover apples. If we use this, it's just a demonstrative pronoun meaning this action which has just been described.
If you're interested, see here for some interesting information about "Participle Adjectives" (such as "interested" and "interesting" as used earlier in this sentence).
Note that there are certain limitations on how adjectival left = remaining can be used...
3: Tom sold 3 of his 10 tickets. How many are left unsold? (either left or unsold could be omitted)
4: There are 7 left
5: There are 7 unsold
6: There are 7 tickets left
7: There are 7 tickets unsold
8: There are 7 unsold tickets
9: *There are 7 left tickets (idiomatically unacceptable)
...where #9 is "unacceptable" even though the basic construction is okay with alternatives which are "synonymous" in context (such as unsold, remaining). Because we're more used to adjectival left before a noun meaning "levo" (on the left, not the right side), we would normally express #9 as...
10: There are 7 leftover tickets (or left-over)
You're right about intonation - it refers specifically to changes in pitch, ie. the "ups and downs" of the voice in the context of a sentence.
Inflection is a tricky word in that it has two very distinct meanings. One of those meanings (the one you've brought up in your post) has nothing to do with prosody or spoken language - instead, it refers to the way the word changes to denote its grammatical attributes (eg. say -> says to denote third person singular). As English is mostly an analytical language there are few cases where inflection is used, but other languages make heavy use of it in their grammars.
The other meaning of inflection is in fact related to speech patterns:
the way in which the sound of your voice changes during speech, for example when you emphasize particular words
It's a more informal meaning, with few linguistics resources using inflection in that context, and there seems to be little agreement between dictionaries what exactly it encompasses - the Cambridge definition quoted above seems to make inflection more general than intonation and include other elements of prosody such as timbre and stress, while Oxford's one is synonymous with intonation:
a change in how high or low your voice is as you are speaking
If you want to be precise, I'd avoid using inflection to describe speech pattern entirely.
Best Answer
Contrary to your first instinct, it may indeed be a passive construction inside a relative clause:
There you have your form of be. Now this relative clause is shortened to a participle clause: