In [a teaser for the new series of Doctor Who](https://www.youtube.com/watch?v=7HaiGKiUuik) the Doctor asks Clara :

> 
> Clara, **be my pal** and tell me... am I a good man ? 
> 
> 
> 

My problem is that in French it simply doesn't have any other sense than the fact that he wants Clara to be his friend, which doesn't make that much sense in this sentence.  

So what does "be my pal" mean in this context? Is it an idiom ?