Не только не разгадал, но и попал в ловушку.

It is the standard Russian pattern for not only ..., but also ....

So:

• Не только не разгадал = not only did he fail to solve/figure it out
• но и попал в ловушку = but also fell into a trap

This structure links two facts, with the second one often sounding like an even worse or more surprising result.

Because the two не are doing different jobs:

1. не только = part of the fixed expression not only
2. не разгадал = the actual negation of the verb, did not solve / did not figure out

So the logic is:

• не только = not only
• не разгадал = didn’t solve it

Put together: Not only did he not solve it...

This is completely normal in Russian. Compare English:

• He not only didn’t solve it, but also got trapped.

English also has two negatives here in a similar way.

Разгадал is:

• past tense
• masculine singular
• perfective
• from разгадать

Basic meaning: to solve, guess, figure out, crack something such as:

• a riddle
• a mystery
• a secret
• someone’s plan

Because it is perfective, it presents the action as a completed whole: solved / figured out.
Here it is negated: не разгадал = didn’t solve / failed to figure out.

If the speaker were female, it would be:

• не разгадала

If plural:

• не разгадали

Russian often leaves the object unstated if it is obvious from context.

So не разгадал can mean:

• didn’t solve it
• didn’t figure it out
• didn’t crack the mystery/riddle/plan

The missing object could be something like:

• загадку = the riddle
• тайну = the mystery/secret
• замысел = the plan/intention

For example:

• Не только не разгадал загадку, но и попал в ловушку.

In your sentence, the speaker simply assumes the listener already knows what was being talked about.

Попал в ловушку literally means got into a trap or fell into a trap.

Breakdown:

• попал = past tense, masculine singular, from попасть
• в ловушку = into a trap

The verb попасть often means:

• to get into
• to end up in
• to fall into
• sometimes to hit/reach depending on context

Here the meaning is clearly ended up in a trap / fell into a trap.

Because after в, Russian uses:

• accusative for movement into something
• prepositional for location in something

Here there is a change of state or movement:

• попал в ловушку = fell/got into the trap

So ловушку is accusative singular.

Compare:

• Он попал в ловушку. = He fell into a trap.
• Он был в ловушке. = He was in a trap.

So:

• в ловушку = into the trap
• в ловушке = in the trap

Russian often omits the subject pronoun when it is clear from context.

Both verbs are in the past masculine singular:

• разгадал
• попал

So the implied subject is something like he, or possibly I/you if the broader context makes that clear, though masculine past tense strongly points to a masculine speaker or referent.

Russian very often says simply:

• Не понял.
• Пришёл поздно.
• Попал в беду.

instead of repeating он, я, etc., when the subject is already understood.

Yes, both are perfective:

• разгадал ← разгадать
• попал ← попасть

Perfective is used because the sentence refers to concrete completed outcomes:

• he did not solve it
• he ended up in a trap

The sentence is not describing an ongoing process; it is summarizing what happened.

If you used imperfective, the meaning would shift and sound more like process, repeated action, or background context. Here Russian wants the result:

• he failed to achieve one result
• and then reached another, worse result

Yes, Russian word order is flexible, but не только ..., но и ... usually stays recognizable as a pair.

Your version is very natural:

• Не только не разгадал, но и попал в ловушку.

You could also say:

• Он не только не разгадал, но и попал в ловушку.

This just adds the explicit subject он.

Other rearrangements are possible for emphasis, but beginners should stick to the standard pattern:

• не только X, но и Y

That is the safest and most natural model to learn.

Very often, yes. In this correlative construction, не только ... но и ... is the standard pairing.

So learners should think of it as a set pattern:

• не только ..., но и ... = not only ..., but also ...

Sometimes in real speech or writing you may see slight variations, but the classic form is exactly what you have here.

So this sentence is a good model:

• Не только не разгадал, но и попал в ловушку.

In the Russian past tense, the verb changes for gender and number.

Masculine:

• Не только не разгадал, но и попал в ловушку.

Feminine:

• Не только не разгадала, но и попала в ловушку.

Plural:

• Не только не разгадали, но и попали в ловушку.

So the sentence you have is specifically masculine singular in form. That is one reason learners often infer an implied he.