Torniamo a patto che abbiano controllato l'ufficio.

A patto che means provided that, on condition that, or as long as.

It introduces a condition that must be met. So the sentence is saying that we return only if that condition is satisfied.

Similar expressions are:

• a condizione che = on condition that
• purché = provided that / as long as

All of these normally trigger the subjunctive.

Because a patto che is one of the expressions that normally requires the subjunctive in Italian.

So after a patto che, Italian uses:

• abbiano controllato = present perfect subjunctive / more commonly called passato congiuntivo

Compare:

• So che hanno controllato l'ufficio. = I know they checked the office.
  
  • Here you use the indicative because it is presented as a fact.
• Torniamo a patto che abbiano controllato l'ufficio. = We return provided that they have checked the office.
  
  • Here it is a condition, so the subjunctive is used.

Because abbiano controllato emphasizes that the checking must be completed before the action in the main clause.

• abbiano controllato = that they have checked
• controllino = that they check / be checking

In this sentence, the idea is that their checking the office must already be done before we return.

So:

• a patto che controllino l'ufficio = provided that they check the office
  
  • more general, less focused on completion
• a patto che abbiano controllato l'ufficio = provided that they have checked the office
  
  • clearly completed beforehand

It is the passato congiuntivo (past subjunctive).

It is formed with:

• the present subjunctive of avere or essere
• plus the past participle

Here:

• abbiano = present subjunctive of avere
• controllato = past participle of controllare

So:

• che abbiano controllato

This tense is often used when the subordinate action is viewed as already completed.

Because controllare normally takes avere in compound tenses.

So:

• hanno controllato
• abbiano controllato
• avevano controllato

all use avere.

You would use essere only with verbs that require it, such as many verbs of movement or reflexive verbs, for example:

• siano andati
• si siano svegliati

Grammatically, torniamo can mean either:

• we return / we are returning
• let's return / let's go back

Without context, both are possible.

In a sentence like this, it is often understood as a present with a future-like meaning:

• we'll return
• we return

But in speech, depending on context and intonation, it could also sound like a suggestion:

• let's go back, provided that they have checked the office

So the exact English choice depends on context.

It refers to they, but Italian often leaves the subject pronoun out because the verb ending already shows the person and number.

• abbiano clearly means they have in the subjunctive.

So Italian does not need loro unless the speaker wants emphasis or contrast.

For example:

• ...a patto che abbiano controllato l'ufficio. = provided that they have checked the office
• ...a patto che loro abbiano controllato l'ufficio. = provided that they have checked the office
  
  • with extra emphasis on they

Yes. Italian allows flexibility here.

You can say:

• Torniamo a patto che abbiano controllato l'ufficio.
• A patto che abbiano controllato l'ufficio, torniamo.

Both are grammatical.

The first version is often more neutral in everyday use.
The second puts more focus on the condition.

Yes. Some close alternatives are:

• a condizione che
• purché
• sempre che

Examples:

• Torniamo a condizione che abbiano controllato l'ufficio.
• Torniamo purché abbiano controllato l'ufficio.

These are similar, though the tone can vary slightly:

• a patto che = provided that, with a strong sense of a stated condition
• a condizione che = on condition that, slightly formal
• purché = provided that / as long as, very common

All of them normally take the subjunctive.

Because in this sentence the speaker is referring to a specific office, so Italian uses the definite article:

• l'ufficio = the office

Italian uses articles more often than English in many cases, and with a concrete noun like this, the article is very natural.

Without the article, controllare ufficio would be incorrect here.

Not always. Ufficio can mean:

• office as a place
• department
• role/function
• sometimes desk/office area in specific contexts

But in this sentence, the most natural meaning is the office as a place or workplace.

So learners should choose the meaning from context, not assume only one translation every time.

In standard Italian after a patto che, yes, hanno controllato would normally be considered wrong, because this expression requires the subjunctive, not the indicative.

So the standard form is:

• a patto che abbiano controllato

not:

• a patto che hanno controllato

A native speaker might sometimes bend rules in casual speech, but for correct Italian, you should use the subjunctive after a patto che.