As far as I can figure out they are all doing a Latin dance this week and the American Smooth.
They all have 2 Latin dances and 1 ballroom left so if the semi final works the same as last year they will all have to do a latin to leave them with one of each.
I think the one to go will be between Patsy, James and Colin. Zoe and Darren seem to be safe based on their popularity with the judges and/or the public. As for the other three...
Patsy - Her amount of public support is a mystery. Surprising bottom 2 two weeks ago, but saved from bottom this week. Anton has huge support which certainly helps. Her dancing is erratic - if she gets the paso I think she could rock it, the jive would probably see her out.
James - Apparently doing the samba which doesn't inspire me with confidence after his jive. To me it just doesn't feel like his kind of dance. News stories may have affected his popularity with average joe public.
Colin - Not as good at latin. His long limbs may work against him in the ccc. Seems to have quite low public support so a low judges score may put him in danger.
There's also an outside chance of Zoe going considering she is doing her less favoured latin. But I have a feeling she could simply stand there, shake her maraccas Julian-style and still get a 10.
In fact, Darren seems to be the only one who is utterly safe! (You know he is so going out after I've typed that - oops!

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Overall, the most likely candidate seems to be Patsy, having been in the bottom 2 two weeks in a row. Pains me to say it as a fan of her and Anton but I'm looking on brightside - I thought they were definitely out this week so getting another week was a huge unexpected bonus! And they'll all be back again for the final.