När huvudpersonen äntligen kom hem, märkte jag att jag hade läst i två timmar utan paus.

This is a very common Swedish word-order pattern.

When a sentence starts with something other than the subject, Swedish usually follows the V2 rule: the finite verb must come in the second position of the main clause.

So here:

• När huvudpersonen äntligen kom hem = a subordinate clause placed first
• then the main clause begins
• in the main clause, the finite verb comes first: märkte
• and the subject comes after it: jag

So Swedish says:

• När huvudpersonen äntligen kom hem, märkte jag...

not:

• När huvudpersonen äntligen kom hem, jag märkte...

This often feels unusual to English speakers, because English keeps normal subject-verb order more often.

A useful comparison:

• Igår läste jag.
• Nu förstår jag.
• När han kom, såg jag honom.

In all of these, something other than the subject comes first, so the verb comes before the subject in the main clause.

Huvudpersonen means the main character.

It is made up of:

• huvud = main, head
• person = person
• huvudperson = main character / main person
• huvudpersonen = the main character

Swedish often adds the definite article to the end of the noun instead of using a separate word like the.

So:

• en huvudperson = a main character
• huvudpersonen = the main character

This is one of the biggest structural differences from English.

In Swedish, kom hem is the normal idiomatic way to say came home.

• kom = came
• hem = home

Just like in English, home often works without a preposition in this kind of expression:

• go home = gå hem
• come home = komma hem

You would not normally say kom till hemmet unless you meant something very specific and unusual, like came to the home/institution.

So kom hem is the natural everyday expression.

Äntligen means finally.

Here it modifies kom hem:

• När huvudpersonen äntligen kom hem...
• When the main character finally came home...

Its position is very natural here, between the subject and the verb phrase.

You may see adverbs like this move around depending on style and emphasis, but this placement is very common:

• Han äntligen kom hem would sound wrong
• När huvudpersonen kom hem äntligen is possible only in special emphatic contexts and is not the normal choice

So for learners, subject + adverb + verb is a good pattern to notice in subordinate clauses like this one.

Att here means that and introduces a content clause: the thing that was noticed.

So:

• märkte jag = I noticed
• att jag hade läst i två timmar utan paus = that I had been reading for two hours without a break

This is very similar to English.

Swedish often uses att where English may use that, even when English might sometimes leave that out.

For example:

• Jag tror att han kommer. = I think that he is coming.
• Hon sa att hon var trött. = She said that she was tired.

In many cases, Swedish can also omit att, but with verbs like märka it is very common and clear to include it.

Hade läst is the pluperfect (also called past perfect): had read / had been reading.

It is used because the reading happened before the moment of noticing in the past.

Timeline:

1. the speaker was reading
2. the main character came home
3. at that moment, the speaker realized something

So Swedish uses:

• märkte = noticed
• hade läst = had read / had been reading

If you said läste, it would sound more like a simple past action, without clearly marking that it was already in progress or completed before the noticing.

Compare:

• Jag märkte att jag hade läst i två timmar.
  = I realized I had been reading for two hours.

• Jag märkte att jag läste i två timmar.
  This is much less natural here and does not express the same time relationship well.

In Swedish grammar, läst in hade läst is usually called the supine, not the past participle.

This is a point that often surprises English speakers.

For the verb läsa:

• infinitive: läsa
• present: läser
• past: läste
• supine: läst
• past participle: läst (same form here, but not always treated as the same grammatical function)

After har, hade, and other forms of ha, Swedish uses the supine:

• jag har läst
• jag hade läst

So even though it looks similar to an English past participle, Swedish grammar usually labels it differently.

Yes, i often means in, but with time expressions it can mean for when talking about duration.

So:

• i två timmar = for two hours

This is a very common Swedish pattern:

• Jag väntade i en timme. = I waited for an hour.
• Hon sov i tio timmar. = She slept for ten hours.
• Vi pratade i flera minuter. = We talked for several minutes.

English speakers often want to use för here, but för två timmar usually means something different, more like two hours ago in some contexts, or it simply sounds wrong for duration.

So for duration, learn:

• i + time period

After utan (without), Swedish often uses a noun without an article when speaking generally.

So:

• utan paus = without pause / without a break

This is very natural Swedish.

Other examples:

• utan problem = without problems
• utan hjälp = without help
• utan tvekan = without doubt

You could sometimes say utan en paus, but that would sound more specific or emphatic, as if you were thinking of one particular break. In this sentence, utan paus is the most natural general expression.

The comma here separates the initial subordinate clause from the main clause:

• När huvudpersonen äntligen kom hem, märkte jag...

This comma is acceptable and helpful for readability, especially in longer sentences.

However, Swedish punctuation is often a bit lighter than English punctuation, and in many cases the comma before the main clause is optional:

• När huvudpersonen äntligen kom hem märkte jag att...

That version can also be correct.

So the comma is not always strictly required, but many writers use it to make the structure clearer.

Yes. In this sentence, När means when and introduces a subordinate clause:

• När huvudpersonen äntligen kom hem = when the main character finally came home

Here it functions as a conjunction.

But när can also be used as an adverb in questions:

• När kommer du? = When are you coming?

So the word is the same, but the function changes depending on the sentence.

In your example, it is clearly introducing a time clause, so it is functioning as a conjunction.

This is about the relationship between events in time.

Swedish is marking two past events as the main timeline:

• huvudpersonen ... kom hem = the main character came home
• märkte jag = I noticed

Then it marks an earlier, background action:

• jag hade läst i två timmar = I had been reading for two hours

So the structure is:

• one past event happened
• at that moment, another past realization happened
• the reading had already been going on before that

This is exactly the kind of situation where Swedish uses the past perfect.

A rough timeline:

• reading starts
• two hours pass
• main character comes home
• I notice how long I have been reading

That is why hade läst is the right form.