Fourth Year Triumphs at Trebizon Boarding School by Anne Digby

'There's something mysterious about her.'
 
When Rebecca, Sue and Tish take up running, they never expect it to leas to an adventure. And that is nothing compared to the shock of a film crew arriving at Trebizon! They film MARGOT surfing, Tish at the beach and even Rebecca's big tennis match.
 
But the friends soon realize that the film company is not what it seems.