```ts
export function capAfter(passage: string): string {
  const sentences = passage.split('. ');
  const capitalizedSentences = sentences.map(sentence => {
    if (sentence.length > 0) {
      return sentence[0].toUpperCase() + sentence.slice(1).toLowerCase();
    }
    return '';
  });
  return capitalizedSentences.join('. ');
}
```