Hễ có manh mối là chúng ta giải đố.

It is a very common Vietnamese pattern meaning something like:

• whenever ... , ...
• as soon as ... , ...
• every time ... , ...

So Hễ có manh mối là chúng ta giải đố means there is a regular or automatic relationship between the two parts:

• hễ có manh mối = whenever there is a clue / whenever we have a clue
• là chúng ta giải đố = then we solve the puzzle/riddle

This structure often suggests that once the first thing happens, the second thing naturally follows.

A similar example:

• Hễ trời mưa là tôi ở nhà.
  • Whenever it rains, I stay home.

Not really.

In this sentence, là is not functioning like the normal to be verb. Instead, it acts more like a connector introducing the result or main clause.

So in hễ ... là ..., là is closer to:

• then
• that’s when
• a clause-linker with no direct English equivalent

That is why you should not read this sentence as Whenever there is a clue is we solve puzzles. That would be the wrong analysis.

Sometimes yes.

You may also see:

• Hễ có manh mối, chúng ta giải đố.

This is understandable, but hễ ... là ... is a very established pattern, so keeping là sounds more complete and natural in many cases.

You may also encounter:

• hễ ... thì ...

For example:

• Hễ có manh mối thì chúng ta giải đố.

That is also possible.

Because có here means to have or there is/there are.

So có manh mối can mean:

• there is a clue
• we have a clue
• a clue appears / becomes available

Vietnamese often uses có + noun in places where English might use:

• there is
• there are
• have

So this part is very natural Vietnamese structure.

Manh mối means clue, lead, or trace.

It is often used when you are trying to figure something out, especially in contexts like:

• mysteries
• investigations
• hidden answers
• problem-solving

It can be broader than just a playful puzzle clue. It can also mean a lead that helps you uncover the truth.

So compared with a very simple word like gợi ý:

• gợi ý = hint
• manh mối = clue/lead, often something more substantial

Giải đố means to solve a riddle, solve a puzzle, or sometimes figure out a challenge/question.

It is a fixed expression:

• giải = solve
• đố relates to riddling/challenging

Depending on context, English translations could be:

• solve the riddle
• solve the puzzle
• figure it out

So even if English uses different words, giải đố is the basic Vietnamese idea of solving something presented as a puzzle or riddle.

No. Giải đố can stand by itself.

Both are possible:

• giải đố = solve riddles/puzzles
• giải câu đố = solve the riddle

The version with câu đố is more explicit, because câu đố means riddle. But giải đố is already a normal, established phrase.

So this is similar to how some verb-object combinations in Vietnamese become common set expressions.

Because chúng ta includes the listener, while chúng tôi excludes the listener.

• chúng ta = we, including you
• chúng tôi = we, not including you

So chúng ta giải đố means the speaker is including the person they are talking to in the activity.

If the speaker meant my group solves the puzzle, but not you, they would more likely say chúng tôi.

Vietnamese does not mark tense on the verb the way English does.

So giải đố itself does not change for:

• solve
• solved
• will solve

The time meaning comes from context, time words, or markers like:

• đã = past
• đang = ongoing
• sẽ = future

In this sentence, because of hễ ... là ..., the most natural reading is a general/habitual one:

• whenever there is a clue, we solve the puzzle
• every time there is a clue, we solve it

Yes, but the nuance changes.

• nếu = if
  More neutral, often for a real condition or hypothetical situation.

• khi = when
  More purely temporal.

• cứ ... là ... = every time ... then ...
  Very common in speech and often more conversational.

• hễ ... là ...
  Strongly suggests a repeated, automatic relationship: once A happens, B follows.

So:

• Nếu có manh mối, chúng ta giải đố = If there is a clue, we solve the puzzle.
• Khi có manh mối, chúng ta giải đố = When there is a clue, we solve the puzzle.
• Cứ có manh mối là chúng ta giải đố = Every time there is a clue, we solve the puzzle.
• Hễ có manh mối là chúng ta giải đố = Whenever there is a clue, we solve the puzzle, with a slightly stronger cause-and-effect feel.

It is grammatically fine, but the naturalness depends on context.

The combination manh mối + giải đố is understandable, but there is a slight nuance issue:

• manh mối often sounds like a clue or lead in a mystery/investigation
• giải đố sounds like solving a riddle or puzzle

So if the context is a game, quiz show, escape room, or clue-based puzzle activity, the sentence works well.

But if the context is more like detective work, a Vietnamese speaker might choose a different verb, such as:

• giải mã
• tìm ra đáp án
• phá án
• lần ra sự thật

So the sentence is not wrong; it just sounds best in a puzzle or riddle-solving context.