Alibi is a Latin word, which means elsewhere. It is used when the accused takes the plea that when the occurrence took place he was elsewhere. In such a situation the prosecution has to discharge the burden satisfactorily. Once the prosecution is successful in discharging the burden it is incumbent on the accused who takes the place of alibi to prove it with absolute certainly. An alibi is not an exception envisaged in the IPC or any other law. It is a rule of evidence recognized by Section 11 of the Evidence Act that facts inconsistent with fact in issue are relevant. However it cannot be the sole link or sole circumstance to bare conviction. When one fact is necessary to the hypothesis of the guilt of the accused, but strikingly absent in the chain of circumstantial evidence, the prosecution case certainly will fail. Because, an alibi the relevancy of which is totally inconsistence with hypothesis that the accused had committed an offence.

When the accused took the plea of alibi the burden of proof lies on him under section 103 of this Act. If a person is charged with murder he is to prove that he was elsewhere. The plea of alibi has to be taken at the earliest opportunity and it has to be proved to the satisfaction of the court.

Where an alleged offense has been committed and the prosecution accuses a person of having committed the same it would be a complete answer to the accusation for that person to plead that he was at that time elsewhere; this has of course no reference to offense in which time or place are not material factors; and if that person succeeds in establishing that plea technically called the plea of alibi he will be entitled to an acquittal. The reason is that what may appear on examination of the defence evidence alone to be proved may turn out really not to be so, viewed in the light of evidence to the contrary adduced by the prosecution.

When to raise the plea of alibi:

In order for a plea of alibi to be effective, it is always wise to make the plea at the earliest possible time in the initial stage of a case; this stage could be at the stage of framing of charge or preliminary hearing. However, in some jurisdictions, there may be a requirement that the accused disclose a defence prior to the trial. On the contrary, jurists in other jurisdictions have held an opinion that the mandatory early disclosure of alibis is unfair, possibly even unconstitutional.

Case Laws:

Lakhan Singh @ Pappu vs The State of NCT of Delhi, Delhi HC Crl Appeal No. 166/1999
The plea of alibi cannot be equated with a plea of self-defence and ought to be taken at the first instance and not belatedly at the stage of defence evidence. In any case, the appellant/accused gives no reason or explanations for not taking this plea of alibi at the earliest opportunity.

Binay Kumar Singh vs The State of Bihar, (1997) 1 SCC 283
We must bear in mind that alibi, not an exception (special or general) envisaged in the Indian Penal Code or any other law. It is only a rule of evidence recognized in Section 11 of the Evidence Act that facts which are inconsistent with the fact in issue are relevant.

(a) When the defence of alibi fails-Failure on the part of accused to establish plea of alibi does not help the prosecution and it cannot be held that the accused was present at the scene of occurrence, the prosecution must prove it by positive evidence. Thus the mere failure on the part of the accused to establish the plea of alibi, shall not lead to an inference that the accused was present at the scene of occurrence.

(b) Non access of husband to show illegitimacy of the child:
Since legitimacy of the child implies a cohabitation between husband and wife. For disproving the legitimacy the husband has to prove that he had no cohabitation with his wife during the probable time of begetting as he was in abroad.

(c) Survival of the alleged deceased:
A is accused of murdering В on 10th August 1996 at Delhi. But A tried to prove and led evidence to show that В was alive on 25th December 2004. Both the facts are relevant under section 11 only because these are not consisting with each other.

(d) Commission of an offence by a third person:
A is charged with the murder of B. A leads evidence that В was murdered by C. This is admissible being inconsistent with fact in issue.

(e) Self-infliction of harm:
A is charged with the murder of B. A proves that В had committed suicide. The evidence is admissible.

(f) Non-execution of document:
A files a suit for recovery of possession against В alleging that he has purchased the land. В leads evidence that the deed of sale was not executed as yet. The fact is relevant.

References
Books
1.The law of evidence by Batuk Lal (Central law agency) 2010
Websites referred
1. http://www.shareyouressays.com/knowledge/section-11-of-the-indian-evidence-act-1872-2/120399
2. https://indianlegalsolution.com/plea-of-alibi/