"I've just had a call from the stables to say my horse _______________ (steal) I can't believe that's happened"
The past perfect tense of the verb 'steal' is not suitable in this sentence. It can be either the Simple Past or the Present Perfect tense.
"The basic meanings of the Past Perfect tense are 'earlier past' and 'completed in the past'. The Past Perfect is common after past verbs of saying and thinking, to talk about things that had happened before the saying and thinking took place".
In English six different tenses are used to talk about the past:
the Simple Past ( I worked)
the Past Progressive ( I was working)
the Simple Present Perfect ( I have worked)
the Present Perfect Progressive ( I have been working )
the Simple Past Perfect ( I had worked )
the Past Perfect Progressive ( I had been working)
Some English tenses express meanings (e.g. completion, continuation,
present importance) which are not expressed by verb forms in all other
We use the Simple Past tense to talk about many kinds of past
events: short, quickly finished actions and happenings, longer
situations, and repeated events.
In general, the Simple Past tense is the 'normal' one for talking
about the past; we use it if we do not have a special reason ( *to
express continuation, present importance etc.) for using
one of the other tenses.
Perfect forms are used especially when we want to suggest a connection between a past event and the present, or between an earlier
and a later past event.
I have worked with children before, so I know what to expect in my new job. (* suggests a connection between past and present)
After I had worked with Jake for a few weeks, I felt I knew him pretty
well. (*shows an earlier and a later past events)
I have done the shopping. What shall I do now? (*suggests the
completion of an event)
(From Michael Swan's PEU)