Perhaps...they are allergic to daisies?

Cute story. I liked how the Doctor and Donna are once again mistaken as being a couple. Also, the last line is really nice. The one thing I would mention is that the plural of "daisy" is "daisies", not daisy's (the apostrophe plus "s" indicates possession).

Aww, very cute. I loved your description of Donna's hat and the metamorphic heads of the aliens! Both Donna and the Doctor were completely in character and I loved how the story was more than the two of them just going to the Planet of the Hats.. because in oneshots like this there often a little too short and a little too sweet. Yours was perfect! I also loved how the people were alredy prepared for the invasion and the Doctor didn't have to save them. He would be disappointed! and how Donna suggests that they follow the Srettor to the next planet; she knows him so well! I also loved the last line, because it's so true:

'The Doctor set the TARDIS in motion; sometimes he thinks Donna has been waiting for him all his life.'

Well done, you should be very proud!

Jay-Jay