My cat keeps on hissing at our other cat?

We accidentally left our calico cat Mitty outside on the porch all night and let her in this morning. Our tabby cat, Opal, usually licks and cleans Mitty and they chase each other around the house and they usually take naps together, but when Mitty came back from outside, every time Mitty came up to Opal, Opal would hiss at her. Now it is almost night time and Mitty keeps on trying to play with Opal, but Opal keeps on hissing at her every time Mitty goes near her. Opal is now hiding under the bed and won't come out. Is it because since Mitty was left outside she smells different from what Opal is used too?